Insects do not synthesize cholesterol; the 3-hydroxy-3-methylglutaryl-coenzyme-A (HMG-CoA) produced by HMG-CoA synthase is transformed to mevalonate by HMG-CoA reductase for the production of non-sterol isoprenoids, which are essential for growth and differentiation. To understand the regulation and developmental role of HMG-CoA synthase, we have cloned a 1658 bp cDNA that encompasses the entire transcription unit of the HMG-CoA synthase gene from the cockroach Blattella germanica. This cDNA clone was isolated using as a probe a partial cDNA of B. germanica HMG-CoA synthase, amplified using the polymerase chain reaction. Analysis of the nucleotide sequence reveals that the cDNA encodes a polypeptide of 453 amino acids (M(r) 50338) that is similar to vertebrate HMG-CoA synthase (74-76% conserved residues). The B. germanica cDNA has been expressed as a fusion protein in Escherichia coli and exhibits HMG-CoA synthase activity. The HMG-CoA synthase transcript was differentially expressed throughout B. germanica development. Analysis of RNA samples from different adult female tissues shows high HMG-CoA synthase mRNA levels in the ovary and lower levels in brain and muscle.