Two distinct genes encode two major isoelectric forms of insecticyanin in the tobacco hornworm, <em>Manduca sexta</em>.

Insecticyanin is a blue pigment found in the epidermis and hemolymph of the tobacco hornworm, Manduca sexta. Two distinct full-length eDNA species were isolated and shown to encode the two major isoelectric forms of insecticyanin, the a form (INS-a) and b form (INS-b). Sequence analysis of the two cDNA clones, pE1-11 and pE3-12, reveals that both contain an 618-bp open reading frame which predicts an 189-amino-acid protein and an 17-amino-acid signal peptide. Comparison of the deduced INS-a and INS-b proteins show 13 amino acid differences, of which six are conserved. Three amino acid substitutions are also found between the deduced INS-b sequence and the sequenced INS-b protein isolated from the hemolymph. Isolation and characterization of live genomic clones revealed that pE1-11 and pE3-12 come from two different genes. Both INS-a and INS-b genes have four exons interrupted by three introns at the same positions. The two genes share 93% nucleotide similarity in the coding region. Moreover, the &#39;TATA box&#39; and &#39;CAAT box&#39; are completely conserved in the putative promoter regions of the two genes. Primer extension revealed that both INS-a and INS-b genes begin their transcription at position -52 relative to their translation initiation codon, ATG. We conclude that the two genes are the result of gene duplication. [ABSTRACT FROM AUTHOR]