a, random mutagenesis; b, site-directed mutagenesis. Underline letters indicate the sequence for ligation-independent cloning; Italic letters indicate the mutation nucleotides. The reverse primers not
aAll sequences are based on the sequence of the J35 isolate (GenBank accession no. AY386330).bGGATCC is a restriction site of BamHI, AAGCTT is a restriction site of HindIII.