Reasons for cleavage of protein after His-tag purification It is important to carry out the cleavage of the resultant protein after a process of His-tag purification as the product may be having a myriad of proteins including raw lysate that originates from the bacterial host. These extra proteins may alter the purity of the resultant protein and affect any experimental procedures carried on the protein thereafter. In addition, some proteins may not have been denatured and as such, cleavage provides a way of getting rid of such resistant proteins. Some proteins possess activity that may, in turn, interfere with the proper application of the purified protein of interest. Cleavage generates different active proteins that can be utilized for different purposes. Furthermore, it acts to remove inactive or toxic residues from the protein of interest creating a pure utilizable protein or enzyme residue. Consequently, the by-products of cleavage may be utilized for different purposes in various industries be it biopharmaceuticals or the sugar industry. Different sizes of proteins after His-tag purification The process of His-tag purification may yield different sizes of pure proteins depending on the concentration of the salt used during the purification processes. High salt concentrations may result in low size proteins while low salt concentration yields proteins with higher sizes than expected. The type of salt also determines the size of the resultant purified proteins. Salts with more divalent cations may result in low-sized proteins. Some purified proteins are held in the flow-through and wash resulting in low-sized purified proteins while an overused or old matrix may result in incomplete purification leading to proteins with a bigger size than expected. Reasons for using cell line BL21 DE3 for expression of protein better than cell line bl21 codon plus The cell line BL21 DE3 has been employed in many purification processes of various forms of proteins. BL21 DE3 cell line is preferred to the cell line BL21 codon plus since it is a very versatile cell line and acts as an all-purpose cell line. In addition, it can be used in processes that entail the purification of advanced-level proteins as it provides an uncomplicated method of initiation of induction. The inductive process when using the BL21 codon plus is tedious and as such, unfavorable during purification of proteins using the His-tag technique. BL21 DE3 cell lines are highly compatible with numerous vector systems. Vector systems such as the pET vector system can be used with ease with this cell line as compared to the BL21 codon plus cell line. Consequently, the BL21 DE3 cell line provides a custom expression of the T7 vectors as compared to the BL21 codon plus cell line that provides for custom expression of non-T7 vectors. Because of these differences, the former is preferred in situations where His-tagging purification is required as a wide variety of vector systems can be employed. 2 There is tighter control of some types of proteins that may be toxic when utilizing the BL21 DE3 cell line. In addition, the cell line can be modified to increase resistance to some types of antibiotics such as chl