The 5' region of YP2 cDNA, a follicular epithelium yolk protein subunit in the moth, Plodia interpunctella, shows that the polypeptide contains an extended internal coding region. Partial cDNA clones for YP2 were isolated from a pharate adult female ovarian cDNA expression library in Lambda Zap II by screening with antigen selected YP2 antiserum. The 5' sequence of the YP2 transcript was determined by 5' RACE PCR of ovarian mRNA using YP2 sequence-specific nested primers. The combined cDNA and 5' RACE sequencing showed the YP2 transcript to be 1971 bp in length up to the poly(A) tail with a single open reading frame for a predicted polypeptide of 616 amino acids. Northern analysis showed a single YP2 transcript to be present in ovarian RNA that was approximately 2 kb in length. The predicted amino acid sequence for YP2 from P. interpunctella is most closely related to egg specific protein (ESP) from Bombyx mori and the partial YP2 sequence from Galleria mellonella. YP2 from P. interpunctella also is similar to vertebrate lipases and contains a conserved lipid binding region. However, the 5' coding region of YP2 from P. interpunctella contains an in-frame insert of approximately 438 bp that had replaced an approximately 270-bp region as compared with ESP from B. mori and YP2 of G. mellonella. This suggests that the insert occurred by a recombinational event internal to the YP2 structural gene of P. interpunctella.