Catalyzes the synthesis of IV-HSL (isovaleryl-homoserine lactone), a quorum-sensing (QS) autoinducer molecule which binds to BjaR1 transcriptional regulator to activate expression of QS-dependent genes. Is active with isovaleryl-CoA but cannot use isovaleryl-ACP as acyl donor. 3-methylbutanoyl-CoA + S-adenosyl-L-methionine = CoA + H(+) + N-isovaleryl-L-homoserine lactone + S-methyl-5'-thioadenosine By IV-HSL via the transcriptional regulator BjaR1. Cells lacking this gene fail to produce IV-HSL. Belongs to the autoinducer synthase family. Extended N-terminus.