CLONING AND NUCLEOTIDE-SEQUENCES OF 2 GENES INVOLVED IN THE 4''-O-ACYLATION OF MACROLIDE ANTIBIOTICS FROM STREPTOMYCES-THERMOTOLERANS

A DNA fragment responsible for the 4''-O-acylation of macrolide antibi otics was cloned from a mutant strain of the carbomycin producer Strep tomyces thermotolerans. The gene encoding the macrolide 4''-O-acyltran sferase was within a 2.7-kb region of the cloned fragment (15-kb). Str eptomyces lividans carrying the region converted exogenously added tyl osin to 4''-O-acyltylosins. Nucleotide sequencing of the region showed two open reading frames (ORFs). Expression assay using deleted plasmi ds showed that both ORFs were essential for optimal expression of the acyltransferase activity. One of them (acyB1) was identical with care reported previously as a gene encoding 4''-mycarosyl isovaleryl-CoA tr ansferase. The other (acyB2) was assumed to encode a novel regulatory protein that could activate acyB1 expression. acyB1 and acyB2 were hig hly conserved among streptomycetes with macrolide 4''-O-acyl transfera se activity.