Functional sequence selection method and functional sequence selection system

A method for making a recombinant gene includes searching a database using a nucleotide sequence of a coding region, a nucleotide sequence that encodes an amino acid sequence, or an amino acid sequence, of a gene, for one or more nucleotide sequences having homology; selecting one or more nucleotide sequences other than nucleotide sequences only derived from a genome from the selected nucleotide sequences; for ones of the selected one or more nucleotide sequences comprising an upstream or downstream nucleotide sequence, analyzing whether the upstream or downstream nucleotide sequence is a functional sequence to select one or more first functional sequences; for ones of the selected one or more nucleotide sequences comprising no upstream or downstream nucleotide sequence, analyzing whether a gene information has any description indicating a functional sequence to select one or more second functional sequences; scoring the selected functional sequences; and selecting one or more functional sequences.

The present application claims the priority to Japanese Patent Application No. 2019-055527 filed on Mar. 22, 2019, which is hereby incorporated by reference.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jun. 26, 2020, is named 126042-005UT1_SL.txt and is 10,262 bytes in size.

TECHNICAL FIELD

The present invention relates to functional sequence selection methods and functional sequence selection systems.

BACKGROUND ART

Promoter and terminator sequences, which are functional sequences necessary for introducing a gene into cells and expressing it therein, differ depending on gene sequences to be introduced or species from which the cells are derived; therefore, finding the best sequence needs trial and error. To solve such a problem, required is tools for designing gene sequences which facilitates designing of genes, in particular, selecting the optimum functional sequence. At present, a plurality of such tools has already been developed.

For example, by the search using a name of a gene of interest in databases of National Center for Biotechnology Information (NCBI) and The International Genetically Engineered Machine Competition (iGEM) in the U.S.A., a tool with which registered documents as well as promoter and terminator sequences can be obtained has been developed (see Patent Document 1; Bates M. et al., ACS Synth. Biol., 6, 12 (2017)). This tool allows users to obtain, by choosing documents of interest by themselves from retrieved information, one or more promoter and terminator sequences mentioned in the document(s). With this tool, it is possible to obtain, from the registered documents, functional sequence information suitable for the gene to be introduced; however, researchers are required to read through the document(s) to choose the sequences. Another tool that provides a feature of automatic selection of a functional sequence appropriate for purposes has also been developed (see Patent Document 2; Nielsen A. A. K. et al., Science, 352, 6281 (2016)).

An object of the present invention is to provide novel functional sequence selection methods and functional sequence selection systems.

SUMMARY OF THE INVENTION

The present invention encompasses the following aspects.

An aspect of the present invention is a functional sequence selection method for making a recombinant gene for expressing a gene of interest in a cell using a database containing one or more data elements comprising a sequence of a gene or a part of the gene, an amino acid sequence encoded by a gene or a part of the amino acid sequence and/or a gene information of the gene, the method including the steps of, in a functional sequence selection system including an input device for inputting, as a query, a nucleotide sequence of a coding region of the gene of interest, an amino acid sequence of the gene of interest, or a part thereof; a selection device for selecting a functional sequence; and an output device for outputting the selected functional sequence: inputting a query with the input device; in the selection device, searching the database, with homologous sequence search means, using a nucleotide sequence of a coding region, a nucleotide sequence that encodes an amino acid sequence, or an amino acid sequence, of a gene of interest, for one or more nucleotide sequences having homology to the nucleotide sequence of the coding region of the gene of interest or the nucleotide sequence that encodes the amino acid sequence of the gene of interest; memorizing, with first sequence list memorizing means, the one or more nucleotide sequences obtained by the search as a first sequence list; removing, with functional sequence selecting means, nucleotide sequences only derived from a genome to select one or more nucleotide sequences other than the nucleotide sequences only derived from a genome; (1) for ones of the selected one or more nucleotide sequences comprising a nucleotide sequence upstream or downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the upstream or downstream nucleotide sequence is a functional sequence to select one or more first functional sequences, and (2) for ones of the selected one or more nucleotide sequences comprising no nucleotide sequence upstream and downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing by search whether the gene information in the data element has any description indicating a functional sequence to select one or more second functional sequences; memorizing, with second sequence list memorizing means, a second sequence list comprising the one or more first functional sequences and the one or more second functional sequences; scoring, with scoring means, the first and second functional sequences in the second sequence list; selecting, with functional sequence selection means, one or more functional sequences at high ranks in the scoring result; memorizing, with functional sequence memorizing means, the selected one or more functional sequences at high ranks; and outputting, with the output device, the selected one or more functional sequences at high ranks. The one or more nucleotide sequences other than the nucleotide sequences only derived from a genome may be obtained by analyzing whether the gene information comprises any keyword representing a nucleotide sequence derived from a genome. The functional sequence may include a promoter sequence, a terminator sequence, and a stop codon. In the case of (1), whether the upstream or downstream nucleotide sequence is a functional sequence may be analyzed using a functional sequence library or the gene information. The first and second functional sequences may be scored according to their frequencies of occurrence or according to the frequency of a given keyword in the gene information in the data element to which each functional sequence is relevant. The method may further include the step of removing one or more functional sequences that are naturally occurring in the gene of interest from the first and second functional sequences before scoring the first and second functional sequences.

Another aspect of the present invention is a functional sequence selection system for making a recombinant gene for expressing a gene of interest in a cell using a database containing one or more data elements comprising a sequence of a gene or a part of the gene, an amino acid sequence encoded by a gene or a part of the amino acid sequence and/or a gene information of the gene, the system including: an input device for inputting, as a query, a nucleotide sequence of a coding region of the gene of interest, an amino acid sequence of the gene of interest, or a part thereof; a selection device for selecting a functional sequence, the selection device including: homologous sequence search means for searching the database, using a nucleotide sequence of a coding region, a nucleotide sequence that encodes an amino acid sequence, or an amino acid sequence, of a gene of interest, for one or more nucleotide sequences having homology to the nucleotide sequence of the coding region of the gene of interest or the nucleotide sequence that encodes the amino acid sequence of the gene of interest; first sequence list memorizing means for storing the one or more nucleotide sequences obtained by the search as a first sequence list; functional sequence selecting means for removing nucleotide sequences only derived from a genome to select one or more nucleotide sequences other than the nucleotide sequences only derived from a genome, (1) for ones of the selected one or more nucleotide sequences comprising a nucleotide sequence upstream or downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the upstream or downstream nucleotide sequence is a functional sequence to select one or more first functional sequences, and (2) for ones of the selected one or more nucleotide sequences comprising no nucleotide sequence upstream and downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing by search whether the gene information in the data element has any description indicating a functional sequence to select one or more second functional sequences; second sequence list memorizing means for memorizing a second sequence list comprising the one or more first functional sequences and the one or more second functional sequences; scoring means for scoring the first and second functional sequences in the second sequence list; functional sequence selection means for selecting one or more functional sequences at high ranks in the scoring result; and functional sequence memorizing means for storing the selected one or more functional sequences at high ranks; and an output device for outputting the selected functional sequence. The one or more nucleotide sequences other than the nucleotide sequences only derived from a genome may be selected by analyzing whether the gene information comprises any keyword representing a nucleotide sequence derived from a genome. The functional sequence may include a promoter sequence, a terminator sequence, and a stop codon. In the case of (1), whether the upstream or downstream nucleotide sequence is a functional sequence may be analyzed using a functional sequence library or the gene information. The first and second functional sequences may be scored according to their frequencies of occurrence or according to the frequency of a given keyword in the gene information to which each functional sequence is relevant. The method may further include the step of removing one or more functional sequences that are naturally occurring in the gene of interest from the first and second functional sequences before scoring the first and second functional sequences.

Another aspect of the present invention is a functional sequence selection method for making a recombinant gene for expressing a gene of interest in a cell using a database containing one or more data elements comprising a sequence of a gene or a part of the gene, an amino acid sequence encoded by a gene or a part of the amino acid sequence and/or a gene information of the gene, the method including the steps of: searching the database using a nucleotide sequence of a coding region, a nucleotide sequence that encodes an amino acid sequence, or an amino acid sequence, of a gene of interest, for one or more nucleotide sequences having homology to the nucleotide sequence of the coding region of the gene of interest or the nucleotide sequence that encodes the amino acid sequence of the gene of interest; removing nucleotide sequences only derived from a genome from the one or more nucleotide sequences obtained by the search or the one or more nucleotide sequences that encode the amino acid sequence obtained by the search, to select one or more nucleotide sequences other than the nucleotide sequences only derived from a genome; (1) for ones of the selected one or more nucleotide sequences comprising a nucleotide sequence upstream or downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the upstream or downstream nucleotide sequence is a functional sequence to select one or more first functional sequences; (2) for ones of the selected one or more nucleotide sequences comprising no nucleotide sequence upstream and downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the gene information has any description indicating a functional sequence to select one or more second functional sequences; scoring the first and second functional sequences; and selecting one or more functional sequences at high ranks in the scoring result.

Yet another aspect of the present invention is a program for causing the functional sequence selection system to perform the functional sequence selection method according to any one of the above. Still another aspect of the present invention is a non-transitory computer-readable recording medium in which this program is stored.

INDUSTRIAL APPLICABILITY

The present invention made it possible to provide novel functional sequence selection methods and functional sequence selection systems.

DETAILED DESCRIPTION OF THE INVENTION

The objects, features, advantages, and ideas of the present invention are apparent to those skilled in the art from the description of this specification. Those skilled in the art can easily reproduce the present invention from the description herein. The embodiments and specific examples described below represent preferable aspects of the present invention, which are given for the purpose of illustration or explanation. The present invention is not limited thereto. It is obvious to those skilled in the art that various modifications and changes may be made according to the description of the present specification within the spirit and scope of the present invention disclosed herein.

A functional sequence selection method according to an embodiment of the present invention is used. Specifically, a functional sequence selection method for making a recombinant gene for expressing a gene of interest in a cell using a database comprising one or more data elements comprising a sequence of a gene or a part of the gene, an amino acid sequence encoded by a gene or a part of the amino acid sequence and/or a gene information of the gene, the method including the steps of: searching the database using a nucleotide sequence of a coding region, a nucleotide sequence that encodes an amino acid sequence, or an amino acid sequence, of a gene of interest, for one or more nucleotide sequences having homology to the nucleotide sequence of the coding region of the gene of interest or the nucleotide sequence that encodes the amino acid sequence of the gene of interest; removing nucleotide sequences only derived from a genome from the one or more nucleotide sequences obtained by the search or the one or more nucleotide sequences that encode the amino acid sequence obtained by the search, to select one or more nucleotide sequences other than the nucleotide sequences only derived from a genome; (1) for ones of the selected one or more nucleotide sequences comprising a nucleotide sequence upstream or downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the upstream or downstream nucleotide sequence is a functional sequence to select one or more first functional sequences; (2) for ones of the selected one or more nucleotide sequences comprising no nucleotide sequence upstream and downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the gene information comprises any description indicating a functional sequence to select one or more second functional sequences; scoring the first and second functional sequences; and selecting one or more functional sequences at high ranks in the scoring result.

A functional sequence selection method of the present invention is performed in a functional sequence selection system described below. Specifically, a functional sequence selection method for making a recombinant gene for expressing a gene of interest in a cell using a database comprising one or more data elements comprising a sequence of a gene or a part of the gene, an amino acid sequence encoded by a gene or a part of the amino acid sequence and/or a gene information of the gene, the method including the steps of, in a functional sequence selection system including an input device for inputting, as a query, a nucleotide sequence of a coding region of the gene of interest, an amino acid sequence of the gene of interest, or a part thereof; a selection device for selecting a functional sequence; and an output device for outputting the selected functional sequence: inputting a query with the input device; in the selection device, searching the database, with homologous sequence search means, using a nucleotide sequence of a coding region, a nucleotide sequence that encodes an amino acid sequence, or an amino acid sequence, of a gene of interest, for one or more nucleotide sequences having homology to the nucleotide sequence of the coding region of the gene of interest or the nucleotide sequence that encodes the amino acid sequence of the gene of interest; memorizing, with first sequence list memorizing means, the one or more nucleotide sequences obtained by the search as a first sequence list; removing, with functional sequence selecting means, nucleotide sequences only derived from a genome to select one or more nucleotide sequences other than the nucleotide sequences only derived from a genome; (1) for ones of the selected one or more nucleotide sequences comprising a nucleotide sequence upstream or downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the upstream or downstream nucleotide sequence is a functional sequence to select one or more first functional sequences, and (2) for ones of the selected one or more nucleotide sequences comprising no nucleotide sequence upstream and downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing by search whether the gene information in the data element comprises any description indicating a functional sequence to select one or more second functional sequences; memorizing, with second sequence list memorizing means, a second sequence list comprising the one or more first functional sequences and the one or more second functional sequences; scoring, with scoring means, the first and second functional sequences in the second sequence list; selecting, with functional sequence selection means, one or more functional sequences at high ranks in the scoring result; memorizing, with functional sequence memorizing means, the selected one or more functional sequences at high ranks; and outputting, with the output device, the selected one or more functional sequences at high ranks.

The present method is described in detail below.

The method according to this embodiment involves first to seventh steps shown in FIG.1. Each of these steps is described in detail below.

A first step, i.e., a query input step1is a step for starting the method by inputting, as a query, a nucleotide sequence of a coding region of a gene of interest that a user wants to introduce into cells, an amino acid sequence of the gene of interest, or a part thereof. Specifically, the query is a sequence consisting of the following (1) or (2), or a sequence comprising the following (1) or (2):

(1) a nucleotide sequence of a coding region of a gene of interest or a part thereof;

(2) an amino acid sequence encoded by the gene of interest or a part thereof.

When a name of a registered sequence is used, a pre-processing of obtaining a gene sequence from its gene name may be performed and the sequence thus obtained may be inputted as a query. Two or more sequences may be inputted as a query; in such cases, however, it is preferable that they are inputted in a distinguishable manner.

In addition, various parameters and options for a second step (a homology search step2), a fourth step (a search result analyzing step4), a sixth step (a scoring step6), a seventh step (a functional sequence region output step7) shown inFIG.1may also be inputted along with the query.

The second step, i.e., the homology search step2is a step for searching, with the nucleotide sequence of the coding region of the gene of interest, the amino acid sequence of the gene of interest, or the part thereof, which was inputted as the query in the first step and given as a search string, for one or more nucleotide sequences or one or more amino acid sequences with a high similarity to the search string. Such homology searches of nucleotide sequences or amino acid sequences of a gene are performed in one or more biological information database containing sequences of genes and/or their subsequences, amino acid sequences encoded by one of genes and/or their subsequences, and/or gene information. As examples of the databases that are often used by researchers, Entrez at NCBI, DDBJ at National Institute of Genetics in Japan, European Bioinformatics Institute (EBI) as part of European Molecular Biology Laboratory (EMBL), LocusLink provided by NCBI, and SWISS-PROT mainly with protein information coverage are widely known. The choice which database is used may be determined in advance or specified along with the query in the first step.

Some known methods of homology searches using a database or databases involve the use of Basic Local Alignment Search Tool (BLAST) or SSEARCH, which are tools for finding similarities of nucleotide sequences or amino acid sequences to queries. These tools may be used to obtain information about a gene sequence with a high similarity to the query. Thresholds for reporting homology may be specified along with the query in the first step. As a threshold for reporting homology, the E value may be used in BLAST.

The term “gene information” as used herein refers to a description of features of a gene. The gene information includes, for example, the name and/or ID of a data element for a sequence registered in a database, information about a document in which the sequence is described (e.g., a part or all of the publication date, abstract, author(s), and nucleotide sequences or amino acid sequences and their origins found in the document).

A third step, i.e., a first sequence list memorizing step3is a step for making a list from the information on sequences with high similarities to the search string retrieved in the second step and memorizing the list. The information compiled as a list include one or more nucleotide sequences, amino acid sequences, or nucleotide sequences that encode an amino acid with high similarities to the search string obtained by the search as well as information about the positions of regions with high similarities to the search string on a nucleotide sequence or on an amino acid sequence, the names and/or IDs of data elements for the sequences in the database, and information about documents in which the sequences are found. The information on the positions of regions with high similarities to the search string may be, for example, the number of nucleotides from the 5′ end of each registered nucleotide sequence but is not limited thereto.

The fourth step, i.e., the search result analyzing step4is a step for classifying the nucleotide sequences and their associated information compiled as a list in the third step into a group for naturally-occurring sequences and a group for other sequences (step4-1), selecting one or more functional sequence regions from the group for other sequences and analyzing them (step4-2), and then classifying the functional sequence region(s) again into a group for naturally-occurring sequences and a group for artificial sequences (step4-3). A flowchart of these step is shown inFIG.2and is described below.

Step4-1: Classification into Naturally-Occurring Sequences and Other Sequences

In this step, the data elements for sequences in the first sequence list10obtained in the third step are divided into a group for naturally-occurring sequences and a group for other sequences which are candidates of artificial sequences, in a naturally-occurring sequence set-aside step11. As used herein, the term “naturally-occurring sequence,” as shown in step12, refers to a nucleotide sequence only derived from one or more genomes, that is, a nucleotide sequence consisting of one or more entire genomes or parts of genomes of organisms, whereas the term “artificial sequence” refers to a nucleotide sequence other than the nucleotide sequence only derived from one or more genomes, that is, a nucleotide sequence comprising a sequence that is not naturally occurring. For the classification, naturally-occurring sequences can be identified by, for example, the presence of one or more keywords in the gene information in the data element for a given sequence retrieved during the homology search, the keywords indicating that the sequence in question is naturally occurring. The applicable keywords include, for example, “complete genome,” “genome,” and “chromosome” but are not limited thereto. The other sequences are those assigned with data elements without any of the above-mentioned keywords. Thus, the data elements other than those for the naturally-occurring sequences can be added to a group for other sequences. Sequences other than the naturally-occurring sequences or sequences assigned with information including one or more keywords indicating that they are artificially designed sequences can be classified as the group for other sequences. The applicable keywords include, for example, “synthesis,” “mutant,” and their synonyms, but are not limited thereto. It is preferable that the data elements in the first sequence list10are classified into a group for naturally-occurring sequences and a group for other sequences in the naturally-occurring sequence set-aside step11and then the functional sequence regions are selected and analyzed in the step4-2; however, the order of the steps is not limited thereto.

Step4-2: Selecting and Analyzing Functional Sequence Regions

Selecting and analyzing the functional sequence regions is a step of selecting one or more regions having one or more functional sequences required for a gene to function in an organism from the sequences added to the other-sequence list13in the step4-1and analyzing the functional sequences. The functional sequences include promoter sequences, terminator sequences, and stop codons but are not limited thereto. The term “promoter sequence” as used herein refers to a nucleotide sequence that is required for the initiation of transcription, lies upstream from the transcription initiation site, such as an upstream region of about 300 bp long, 100 bp long, or 60 bp long from the transcription initiation site, and is responsible for the binding of basal transcription factors such as RNA polymerases.

A specific method of analyzing functional sequence regions involves examining whether a nucleotide sequence lies downstream of a region homologous to the nucleotide sequence used for the search or the nucleotide sequence that encodes an amino acid sequence used for the search (a functional sequence region selecting step14), but different analysis methods are used depending on the results.

In the case that a nucleotide sequence lies upstream or downstream of the region homologous to the nucleotide used for the search or the nucleotide sequence that encodes an amino acid sequence used for the search, a certain length of nucleotide sequence from either end of the coding sequence is selected and is subjected to an analysis to determine whether the selected region have one or more functional sequences, as shown in a functional sequence region selecting and analyzing step15inFIG.2. The term “upstream” and “downstream” as used herein refer to upstream and downstream sides, respectively, immediately adjacent to or away from the region homologous to the query sequence. The upstream region may span upstream from the region homologous to the query sequence, upstream from the start codon, or upstream from the transcription initiation site. The downstream region may span downstream of the region homologous to the query sequence, at a stop codon and downstream therefrom, or downstream of the stop codon. The certain length of the sequence is between 3 bp and 10,000 bp long. The certain length is preferably between 10 and 500 bp long, and more preferably between 20 and 200 bp long. The length of the sequence can be selected independently for the upstream and downstream. The sequences thus selected typically have a promoter sequence on the upstream side and a terminator sequence and/or a stop codon on the downstream side. The methods of analyzing these sequences include those involving: searches for promoter sequences and terminator sequences in one or more functional sequence databases and/or sequences that are commercially used (indicated as “DB” in the functional sequence region selecting and analyzing step15inFIG.2), inferring promoter and terminator sequences using a program for inferring functional sequences (indicated as an inference tool in the functional sequence and analyzing step15inFIG.2), or determining whether the selected sequence has other genetic code sequence(s) and, if any, setting the sequence other than the subject region as a functional sequence (indicated as others in the functional sequence region selecting and analyzing step15). Known databases used in the method of identifying the functional sequences using DB include, for example, Regulon DB and iGEM. As sequences that are commercially used, pieces of information of products provided by Addgene, Gene Scan, TaKaRa Bio Inc., Thermo Scientific, and Invitrogen can be checked. In this case, a functional sequence library comprising various databases and commercial information can be produced to identify sequences that exactly match or similar to the query. As an identification method using an inference tool, inference using a machine learning approach can be used. Known methods include CNN promoter, Findtermtopic=index&group=programs&subgroup-deeplearn), Findterm. Inference can be made using this technology or a program obtained by modifying this technology. Another method of determining whether the selected sequence has other gene sequence(s) involves searching the selected sequence as a query in the BLAST and/or SSEARCH database(s). A region that encodes the gene sequence is identified by the search, and sequences other than that region can be selected as functional sequence regions. In the case that it is described in a gene information, the information may be used; alternatively, functional sequences may be selected from documents using a text mining technique. The text mining technique is described later.

In the case that no sequence lies upstream and downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid sequence which is used for the search, a method of selecting functional sequences from documents using a text mining technique is used, as shown in a functional sequence region analyzing step16inFIG.2. For example, in the case that a gene sequence with a higher similarity to the query is described in a patent document, information about the patent document in question and ID information for the gene sequence found in that document are described in the gene information. Thus, text strings and paragraphs with the ID of that sequence in the entire patent document are scanned to determine whether an associated keyword or keywords are found. If any, by retrieving the keyword(s), information about a promoter or terminator sequence can be obtained. The keywords include “promoter” and “terminator.” These words and the nucleotide sequence(s) in the same document can be selected. Other than the keywords just mentioned, the name of a promoter, terminator, vector, or plasmid may be described. In such cases, it is possible to select sequence information by generating a functional sequence library in which the above-mentioned name(s) and the nucleotide sequence information are stored, based on the information about databases and commercial products, as in the searches in DB in the functional sequence region selecting and analyzing step15.

In this step, it is preferable that a stop codon is also searched for as a functional sequence. The stop codon can be outputted in the sixth step in the case that searches against the three nucleotides at the 5′ end of the selected downstream nucleotide sequences provide one or more DNA sequences that are registered as stop codons (TAA, TAG, and TGA), in both of the functional sequence region selecting and analyzing step15and the functional sequence region analyzing step16. In the case that none of these three sequences is present, no stop codon may be presented as the output or the sequence may be presented with TAA being added as the stop codon.

Among the functional sequences, start codons are typically three nucleotides at the 5′ end of the nucleotide sequence entered as the query. Thus, it is determined whether the three nucleotides at the 5′ end of the query starts from the start codon described below, and if the start codon is found, then it is selected. Eukaryotic nucleotide sequence that encodes start codons is normally ATG but in prokaryotes, GTG and TTG are known in addition to ATG.

Step4-3: Re-Classification as Naturally-Occurring Sequences and Artificial Sequences

A database is generated by combining the selected functional sequences for each of the case where a sequence is found in a region upstream or downstream of a region homologous to query and the case where no sequence is found in the upstream and downstream regions.

As an option for the database, the functional sequence regions selected and analyzed in the step4-2and their information can be divided again as follows. A functional sequence region classified as the sequence other than the naturally-occurring sequence can be added to a naturally-occurring sequence list18as a naturally-occurring sequence in the case that the subject functional sequence region has the same sequence as one of the sequences classified as the naturally-occurring sequence (a re-classification step17), and the remaining sequences can be added to an artificial sequence list19; alternatively, these sequences may be added to a second sequence list20without dividing them into two groups.

A fifth step, i.e., a second sequence list memorizing step5is for making a second sequence list20from the functional sequence region information added to the artificial sequence list19obtained in the fourth step, as shown inFIG.2, and memorizing the second sequence list20. Information of the data relevant to the first sequence list as well as methods of selecting and analyzing functional sequences can be added to the list along with the sequences. In particular, when functional sequences are identified using a database during the analysis of them, it is preferable that the names of the database and the sequence from which information is obtained are also added to the list.

The sixth step, i.e., the scoring step6is for scoring the functional sequences in the second sequence list obtained in the fifth step from a desired perspective. The desired perspective may be, for example, frequency. In this case, the number of each data elements in the second sequence list20is used as a score, and the data element that is largest in number is considered as the one at a top rank. A promoter sequence, a terminator sequence, or a sequence pair in that data element is presented. Another desired perspective involves a function required for a functional sequence. For example, when functional sequence information required for a gene to impart a function of synthesizing a certain substance to an organism is examined, functions such as 1. the species to which the gene is to be introduced, 2. whether or not the substance of interest has been synthesized, and 3. the amount of the introduced gene (expression level) in an organism are associated. In such cases, keywords related to the 1, 2, and 3 are given along with the query in the first step, and frequencies of occurrences of these keywords in the information in question are determined in the fourth step, and the numbers of the counts obtained can be presented from the largest as scores. The keywords used as queries may be a keyword other than those for the above-mentioned 1, 2, and 3. In addition, the information against which the keyword searches are made include, for example, the names of data and documents, but are not limited thereto.

The seventh step, i.e., the functional sequence region output step7is for selecting one or more functional sequence regions at high ranks based on the scoring performed in the sixth step and outputting them. The functional sequence regions may be outputted as a list. It is desirable that the nucleotide sequences selected here are one or more functional sequences selected from the group of promoter sequences or regions, the gene sequence (including the start codon) used as the query, stop codons, and terminator sequences or regions. The promoter sequence region as used herein refers to a region between a promoter sequence and the start codon, or a region composed of a promoter sequence and an additional sequence added to the promoter sequence on its upstream side. In the case that the additional sequence is predetermined, this sequence may be added to the promoter sequence on its forward or backward end when the promoter sequence is outputted. This condition can be specified along with the query in the first step. For example, in eukaryotes, a Kozak sequence or a TATAbox sequence can be added between the promoter sequence and the start codon. Prokaryotes are also known to have a consensus sequence. An appropriate sequence may be added depending on the species. As in the promoter sequence region, an additional sequence may be added to a terminator sequence region on its forward or backward end. In the case that the additional sequence is predetermined, this sequence may be added to the terminator sequence on its forward or backward end when the terminator sequence is outputted.

==Method of Designing Expression Vectors==

The functional sequences selected by the functional sequence selection method are ligated to the forward and backward ends of the gene of interest and inserted into the appropriate position downstream of the enhancer of an expression vector. As a result, an expression vector with a high expression level of the gene of interest can be produced.

Thus, in constructing expression vectors, it is possible to select functional sequence region information automatically and extensively without limiting gene sequences and species of organisms by selecting sequence information from one or more databases using the functional sequence selection method disclosed herein. Furthermore, in the case that a gene is introduced for a specific purpose, it is possible to select a functional sequence that is the best choice for that purpose by entering the functional sequence information suitable for the purpose beforehand along with a query for scoring, which allows users to automatically obtain the optimum functional sequence information in a short period of time. By constructing an expression vector using an obtained functional sequence, it is possible to construct the best expression vector in introducing a gene.

A functional sequence selection system according to this embodiment is for performing the first to seventh steps of the functional sequence selection method. The system includes an input device for inputting, as a query, a nucleotide sequence of a coding region of the gene of interest, an amino acid sequence of the gene of interest, or a part thereof; a selection device for selecting a functional sequence, the selection device including: homologous sequence search means for searching the database, using a nucleotide sequence of a coding region, a nucleotide sequence that encodes an amino acid sequence, or an amino acid sequence, of a gene of interest, for one or more nucleotide sequences having homology to the nucleotide sequence of the coding region of the gene of interest or the nucleotide sequence that encodes the amino acid sequence of the gene of interest; first sequence list memorizing means for storing the one or more nucleotide sequences obtained by the search as a first sequence list; functional sequence selecting means for removing nucleotide sequences only derived from a genome to select one or more nucleotide sequences other than the nucleotide sequences only derived from a genome, (1) for ones of the selected one or more nucleotide sequences comprising a nucleotide sequence upstream or downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing whether the upstream or downstream nucleotide sequence is a functional sequence to select one or more first functional sequences, and (2) for ones of the selected one or more nucleotide sequences comprising no nucleotide sequence upstream and downstream of a region homologous to the nucleotide sequence or the nucleotide sequence that encodes an amino acid used for the search, analyzing by search whether the gene information in the data element has any description indicating a functional sequence to select one or more second functional sequences; second sequence list memorizing means for memorizing a second sequence list comprising the one or more first functional sequences and the one or more second functional sequences; scoring means for scoring the first and second functional sequences in the second sequence list; functional sequence selection means for selecting one or more functional sequences at high ranks in the scoring result; and functional sequence memorizing means for storing the selected one or more functional sequences at high ranks; and an output device for outputting the selected functional sequence. A specific system is described in detail below.

FIG.3shows a block diagram of a gene design system30of one embodiment. The functional sequence selection system of this embodiment is composed of an input/output terminal31as the input device with which users enter queries; the Internet32used for accessing this system; an information controller33that serves as the interface as the output device to present queries and output information; a query introduction part34that introduces a query into the system; a database search part36that performs, as the homologous sequence search means, homology searches with queries using a biological information database35; a search result holding part37that stores homology search results with queries as the first sequence list memorizing means; a functional sequence library38and a search result analyzing part39used for analyses as the functional sequence selecting means; an analysis result holding part40(second sequence list) for holding analysis results as the second sequence list memorizing means; a score analyzing part41for scoring, as the scoring means, based on the data in the analysis result holding part40; and an output controller42for selecting output information based on the score analysis results as the functional sequence selection means and the functional sequence memorizing means. The analysis results are displayed by the output controller42via the information controller33.

In the database search part36, the search result holding part37, the search result analyzing part39, the analysis result holding part40, and the score analyzing part41, the second step (homology analysis step2), the third step (the first sequence list making step3), the fourth step (search result analyzing step4), the fifth step (second sequence list making step5), and the sixth step (scoring step6) inFIG.1are successively performed. Details thereof are found in the above-mentioned description of these steps. The functional sequence library means a library in which the names of promoters, terminators, vectors, and plasmids and their sequences are listed and details thereof are found in the description of the step4-2.

A functional sequence selection method using this system is now briefly described. First, in the functional sequence selection system of this embodiment, the query introduction part34receives information about a gene sequence and conditions for search, analysis, scoring, and output entered by a user with the input/output terminal31. The query introduction part34introduces a query and its associated information to the database search part36, the search result analyzing part39, the score analyzing part41, and the output controller42. The database search part36performs homology searches in the biological information database35via the query introduction part34, with the information about a gene sequence and search conditions as search keys and stores the results in the search result holding part37as a first sequence list. At that time, the kind of the biological information database35and the threshold for reporting homology can be inputted as search conditions. Next, the search result analyzing part39classifies the data elements in the search result holding part37into a group for naturally-occurring sequences and a group for artificial sequences to select and analyze functional sequence regions using the analysis conditions introduced via the query introduction part34as keys, and if necessary, re-classifies the sequences other than the naturally-occurring sequences. The search result analyzing part39stores the results thereof in the analysis result holding part40as the second sequence list. At that time, the nucleotide length of the selected functional sequence region can be inputted as a parameter for analysis. Furthermore, the database to be referred to during the analyses of the functional sequences can be performed referring to information in the functional sequence library38. Moreover, the score analyzing part41scores the data elements in the analysis result holding part40using a scoring method specified via the query introduction part34as the key. At that time, the frequency or a keyword related to a desired function can be specified as a scoring method. One or more functional sequences or regions at high ranks obtained here and the gene sequence of the query can be displayed from the output controller42via the information controller33. Here, as an output condition, in the case that there is one or more sequences that the user wants to add to a functional sequence region, the sequence(s) can be used as a query; in such a case, the user can achieve this by entering the condition into the input/output terminal31.

[1] This embodiment describes an exemplified implementation of the method from the first step to the second sequence list making step which is the fifth step, using the gene design system shown inFIG.3that is fundamentally based on the gene design method shown inFIG.1.

Hereinafter, a detailed description is made with reference toFIGS.4to6.FIG.4shows a search interface.FIG.5shows a flowchart from the first step via the step4-1to the functional sequence region selection in the step4-2, andFIG.6shows a flowchart from the functional sequence region analysis in the step4-2to the fifth step.

First, a query input step60is performed in response to an entry of a query on a search interface50. A user can directly enter an amino acid sequence of a gene, which is a query of this embodiment, into a gene sequence input area51or enter a text file containing the query sequence into an area52. In addition, since searches are performed in a BLAST search61for a homology search step, the user chooses one or more biological information databases62and specifies a threshold for reporting homology on the interface as search options for the information associated with the query which are used in this step. In this embodiment, tBLASTn is used for the BLAST search61. The user chooses the Nucleotide collection of NCBI or a patent sequence database as the biological information databases62at a database option field53and enters an e-value as a threshold for reporting homology54. In addition, the user can choose the length of the nucleotide sequence for functional sequence regions used in the step4-2in a sequence length option field55on the screen. After choosing these options by entering them, the user clicks on a search start button56on the interface. In response to this, a homology search starts and the subsequent steps are performed automatically.

The BLAST search61is performed and search results are added to a first sequence list63. Then, a keyword search64is performed for the added data elements to determine whether a given data element has “complete genome” or “chromosome” in its data name. Data elements that have the keyword are added to a naturally-occurring sequence list66and those that do not have it are added to an other-sequence list65. In this way, the step4-1is performed.

Next, a homology analysis is performed using the other-sequence list65in a selecting step67to generate alignments between the sequences in the list and the search string and thereby to select sequences upstream and downstream of a region homologous to the nucleotide sequence encoded by an amino acid sequence used as the query. Then, a frame check step69is performed to examine whether a frame of each selected sequence lies on the same strand (plus) as the nucleotides coding the amino acid sequence of the query or on the complement strand (minus) using a biological information database68. Then, the frame information may be added to the first sequence list by referring it. In the case that the frame is on the minus strand, a reverse nucleotide sequence relative to the nucleotide sequence that encodes the amino acid sequence used as the query is displayed in which the orientation of the sequence is inverted relative to the query. Thus, a complementary sequence matching step70is performed for the selected sequences. After the positions at which the frames start are made coincide among sequences, it is determined whether the 5′ end of the selected downstream sequence has a stop codon (71), and these changes and additional information are added to the other-sequence list (72). In this way, the step4-2is performed to select the functional sequence regions.

Subsequently, after the functional sequence regions are selected and stored in an other-sequence list80, it is determined whether each of the data elements have an upstream or downstream selected sequence (81). Steps with and without an selected sequence are described.

In the case that one or more selected sequences are present, the selected sequences and their information in the database(s) are stored in a functional sequence library82and searches are made based on these data (83). In this embodiment, the names of promoters, terminators, vectors, and plasmids and their sequences registered in the RegulonDB, iGEM, and Addgene databases are stored in the functional sequence library82. Additional data can be entered into this library. For example, the above-mentioned pieces of information provided by Snap Gene, Invitrogen, and Takara Bio Inc., which are commercially used, can be stored. For sequences retrieved in a search result check step84for searches in DB83, change data is added to the other-sequence list (85). Sequences that do not match in the database are then subjected to identification of a functional sequence by searches with an inference tool86. As this tool, CNNpromoter or Findterm is used. Sequences that do not match in a search result check step87for searches with an inference tool86are then subjected to identification of a functional sequence by another search88. For this another search, BLAST is used to determine whether the selected sequence has a region encoded as a gene sequence. In the case that a region homologous to the gene sequence region is found in a search result check step89for another search88, change data is added to the other-sequence list with the sequence region other than the gene sequence region considered as the functional sequence region. In the case that no such a region is found, change data indicative of this is added to the other-sequence list.

In the case that no selected sequence is present, functional sequence region information is selected by a machine learning technique based on the gene information contained in the first sequence list (90). Specifically, using information about documents in which data are described, searches are made with a sequence ID for patent documents and data name for academic documents to select one or more descriptions of the name of a promoter, terminator, vector, or plasmid from texts or sentences where the information in question is described. An example of this is shown inFIG.7.

InFIG.7, sequence information is selected from patent documents using this tool, with an amino acid sequence of ispE gene, which is an enzyme involved in the MEP pathway ofE. coli, as a query. First, for example, patent document information100as shown inFIG.7is selected by the homology search61inFIG.5. Here, a data name with similarity101, a homologous sequence102, a database sequence ID103, and frame information104are obtained. These pieces of information are stored in the first sequence list. From the data name101and the sequence ID103on the database obtained here, the patent document information and information about the sequence IDs found in that patent document are obtained. For the data shown inFIG.7, the data name101indicates the patent document information “U.S. Pat. No. 6,235,514” and the presence of an exact match with the query sequence in the sequence ID (SEQ ID) No: 5 (of U.S. Pat. No. 6,235,514) in the document. The search term used here is “SEQ ID No: 5” (of U.S. Pat. No. 6,235,514). Based on these pieces of information, searches are made for text strings with SEQ ID No: 5 (of U.S. Pat. No. 6,235,514) in the existing patent documents. An image of a search is shown inFIG.8A. A text string is highlighted by extending forward and backward from the term SEQ ID NO: 5 (of U.S. Pat. No. 6,235,514) in a patent specification109and the highlighted area110is scanned with keywords contained in the functional sequence library111. In the case shown inFIG.8A, the word “pBAD TOPO TA” in the highlighted area110is contained in the functional sequence library as a vector name. With this information, a data entry112with a promoter name and a terminator name can be obtained. In this way, the functional sequence regions can be selected from the patent document. An example of such functional sequence library113is shown inFIG.8B. The functional sequence library113contains a vector name or a plasmid name, the names of a promoter and a terminator and their sequence in that region, information indicating whether these sequences are naturally-occurring or artificial, and data sources. Such libraries are constructed using data selected from the existing databases of promoter, terminator, vector, and plasmid sequences, and from documents describing information about commercially available products. The functional sequence region information thus obtained is added to the other-sequence list as change data (85), as in the case where an selected sequence is found. The analysis of the functional sequence region in the step4-2is performed by this step.

Next, using a genome database or the like, it is determined in a search result check step91where functional sequence and region identical to those in the naturally-occurring sequence list are found in the other-sequence list. If any, they are removed from the other-sequence list (92); if not, the contents of the other-sequence list are classified as an artificial sequence list (93). The obtained artificial sequence list is stored as a second sequence list94. As apparent from the above, by entering an amino acid sequence of a gene that a user wants to introduce as a query, it is possible to obtain functional sequence regions used upon the gene introduction as the second sequence list.

[2] This embodiment describes an exemplified implementation of the method from the fifth step to the seventh step, using the gene design system shown inFIG.3that is fundamentally based on the gene design method shown inFIG.1.

FIG.9is a flowchart showing the fifth step, the scoring step of the sixth step, and the functional sequence region output step of the seventh step.FIG.10shows an output result display interface. The scoring method is chosen, in entering a query in the first step, on which is used, frequency or a keyword under desired conditions. This choice can be made with the option57for the scoring method on the search interface shown inFIG.4.

In the case that scoring by frequency is chosen in a scoring method choosing step121inFIG.9, frequency scoring is carried out for the information on the number of the registered elements in a second sequence list120. The results are stored in a frequency scoring result list (122). In the case that frequency scoring is not chosen, the percentage of appearance of a desired scoring keyword is used for the scoring. The keyword for this scoring can be entered with the option57for the scoring method inFIG.4. In a keyword scoring step123, the documents or data names in the gene information are searched on whether this keyword entered here is present and the number of the keywords is counted as a score. Based on this score, a keyword score result list is made (124). Regardless of which scoring method is used, elements at high ranks in the obtained results are outputted. The functional sequences, i.e., the nucleotide sequences of the gene sequence entered as the query, including the promoter, terminator, stop codon, and/or start codon, are selected as output data in a functional sequence region output step125, and the results are displayed on an interface shown inFIG.10(126).FIG.10shows an example of a representation of an output result130for the elements at higher ranks at the bottom of the search interface. A promoter sequence, a nucleotide sequence of a gene, a terminator sequence, and a promoter-terminator pair sequence are displayed. By clicking pop-up buttons131,132,133, and134for the respective display areas, pop-up windows for them are displayed as shown inFIGS.11,12,13, and14.

First, when the pop-up button131is clicked for the promoter sequence, as shown inFIG.11A, promoter names140and promoter region sequences141which are obtained upon the identification with the specified condition; discriminators142indicating which class of a naturally-occurring sequence (denoted by “N” in the figure), an artificial sequence (denoted by “A” in the figure), or both (denoted as “N/A” in the figure) each sequence belongs to, sequence identification methods and database information143used for the identification, and the frequency scores144are shown. As the sequence identification methods, there are a DB method referring to a functional sequence library, a method using an inference tool, and other methods. In the case that regions are identified with the DB method, the database name in the functional sequence library is displayed. In the case that the regions are inferred with the inference tool method or other method, the inference tool or others (indicated by a hyphen in the figure) is displayed. Then, the artificial sequence with the highest score is displayed at the top of the scoring list. It is also possible to change the arrangement of the results displayed inFIG.10by clicking on a check box145inFIG.11and clicking a select button146. Furthermore, by clicking a display-all button147, all the results obtained by the searches can be displayed (display all results148) as shown inFIG.11B. This operation is also possible to pop-up windows for the terminator sequences shown inFIG.12and for the promoter-terminator sequence pairs shown inFIG.13. Moreover,FIG.14shows a pop-up window for a nucleotide sequence170of the gene entered as the query for this analysis, with the start codon171at the 5′ end and a stop codon172at the 3′ end. A query coverage173is also displayed, and the nucleotide sequence with the query coverage of 100% is displayed inFIG.10and this pop-up window. In this way, for each sequence, sequences at high ranks or arbitrarily selected sequences are displayed inFIG.10, and by clicking a download button135, a gene sequence having a promoter sequence181, the start codon182, and a stop codon183, and a terminator sequence184can be displayed at once, as shown in an output sequence180inFIG.14. With the second sequence list190in which the functional sequence region(s) for an amino acid sequence of a gene that a user wants to introduce into cells, the promoter191and/or terminator sequence(s)194which are functional sequences can be identified or inferred, and optimum functional sequence information can be obtained automatically by scoring with a desired condition. As described above, this tool makes it possible to reduce the time required for designing gene sequences.

An embodiment of the present invention is a program for causing the above-mentioned functional sequence selection system to perform the above-mentioned functional sequence selection method. In addition, a recording medium in which this program is stored in a computer-readable manner is also an embodiment of the present invention. With them, the above-mentioned functional sequence selection method can be made widely available and versatile.

EXAMPLES

Hereinafter, the present invention is described more specifically based on examples, but the present invention is not limited thereto. Those skilled in the art can change the present invention to various embodiments without departing from the spirit of the present invention, and these changes are also encompassed in the scope of the present invention.

The examples below show that functional sequences were obtained through the steps shown inFIG.6with a specified query.

Database searches (83) inFIG.6made with the following conditions provided RegulonDB: ispFp2 as a promoter and (iGEM:BBa_B0010) as a terminator.

Amino acid sequence of a gene, which is one of the queries: gene of non-mevalonate pathway, ispF

Biological information database: choose databases for nucleotide collection and patent sequences

Length of upstream and downstream obtained sequences: 1000 bp

Database searches (83) inFIG.6made with the following conditions provided no functional sequence. Accordingly, blast searches (88) were made. Then, a gene coding region “hypothetical protein AC239_22870” was detected at positions 196 to 804 nt from the 5′ end of an upstream selected nucleotide sequence (1000 nt) and a lac promoter sequence was detected in the remaining sequence of 196 nt.

Amino acid sequence of a gene, which is one of the queries: gene of non-mevalonate pathway, ispG

Biological information database62: choose databases for nucleotide collection and patent sequences

Length of upstream and downstream selected sequences: 1000 bp.