ABSTRACT
ObjectiveTo establish a mutation library of rifampicin resistance gene rpoB. MethodsThe ΔrpoB attB：：rpoB strain of Mycobacterium smegmatis （M. smegmatis） be constructed by homologous recombination and L5 attB phage integration site exchange. Based on the L5 attB plasmid exchange system and resistance selection medium， 48 clones are selected to verify plasmid replacement efficiency. Degenerate primers are designed every 3 bases in the rifampicin resistance determining region （RRDR）， and a full-coverage mutation library of 81 bases in RRDR region is obtained by PCR amplification. The library fragments are seamlessly cloned into the vector and transformed into Escherichia coli （E. coli）to form an E. coli mutation library. Based on the principle of plasmid exchange， the mutant plasmid library is transformed into the M. smegmatis strain ΔrpoB attB：：rpoB， and the original L5 attB site plasmid is replaced to form the M. smegmatis mutant library. The genotype of the library are determined by genome extraction， library construction and high-throughput sequencing. ResultsCompared with the wild-type rpoB gene （5 600 bp）， the amplified fragment of the rpoB knockout strain is 2 200 bp， which proved that the ΔrpoB attB：：rpoB conditional knockout strain of M. smegmatis is successfully constructed. The success rate of plasmid replacement is 100%. There were 540 kinds of single amino acid mutations in both E. coli library and M. smegmatis library， 5 301 kinds of multi-point mutations in E. coli library， and 853 kinds of multi-point mutations in M. smegmatis library. The correlation coefficient between E. coli library and M. smegmatis library is 0.84. ConclusionsWe have developed a strategy to construct a library of mutants targeting the essential mycobacterial gene rpoB， and successfully established a mutant library of rifampicin resistance gene rpoB.