## 1 Introduction
Stated concisely, strains with rudimentary cellulase systems could partially digest cellulosic feedstocks, but the complete conversion of crystalline substrates without the addition of exogenous cellulases remains elusive. Therefore, additional advancements and rapid utilization of lignocellulosic sugars by fermenting microorganisms in industrially relevant conditions are needed before adopting engineered yeasts for commercially viable bioconversion on an industrial scale. However, the scope for additional genetic manipulations in these strains is often limited because of the use of traditional vectors that curb further engineering due to a lack of available markers. To direct the metabolic flux towards products of interest, strain improvement through metabolic engineering may require multiple rounds of genetic changes, such as (i) the introduction of heterologous genes or whole metabolic pathways, (ii) the complete or partial elimination of the activity of some endogenous proteins and/or (iii) the overproduction of certain endogenous proteins [13]. To enable CBP conversion of lignocellulosic sugars to products of interest, many genetic changes must be engineered into this yeast. While several methods to enable genetic engineering in yeasts have been developed over the past four decades, multiple changes often require multiple rounds of engineering that become cumbersome or even impossible due to a lack of appropriate vectors or selection markers. The genetic malleability of _S. cerevisiae_ is greatly aided by a preference for homologous recombination (HR) over non-homologous end joining (NHEJ) for double-stranded break (DSB) repair [14]. Researchers have taken advantage of _S. cerevisiae_'s preference for HR, as it allowed for site-specific integration of foreign genetic material into the yeast genome to produce desired recombinant yeast strains. The development of the CRISPR-Cas9 system for genome editing through the introduction of targeted DSBs and subsequent break repair has resulted in the publication of numerous studies showing a broad range of applications, including gene knockouts as well as knock-ins [15; 16; 17]. Several methods for editing _S. cerevisiae_ using CRISPR-Cas9 systems have been established. The bulk of them utilize different constructs to express the gRNA and Cas9 endonuclease. The development of multi-copy integration of heterologous genes in the yeast _S. cerevisiae_ using the CRISPR-Cas9 genome editing tool has been revolutionary. It has facilitated the development and advancement of yeast cell factories capable of con verting a wide range of substrates into a wide range of products ranging from fuels and chemicals to drugs [3]. In this study, we tested the effect of integrating cellulase encoding genes in various genomic loci in single or multi-copy, in lab and industrial strain backgrounds. We observed variation in the activities obtained when genes were integrated into different loci and that this changed for different reporter genes. Using this knowledge, we created strains with a rudimentary cellulase system that were able to hydrolyze crystalline cellulose. Due to the marker-free nature of CRISPR-Cas9 engineering, subsequent manipulation of these strains is also possible.