Insect immunity. Isolation and sequence of two cDNA clones corresponding to acidic and basic attacins from Hyalophora cecropia

The Cecropia moth has three known classes of antibacterial immune proteins, attacins, lysozyme and cecropins (earlier referred to as P5, P7 and P9, respectively). Six attacins with different isoelectric points have been purified. The N-terminal sequences for five of these forms imply that only two different genes exist. We have now isolated and sequenced two cDNA clones, one for the basic attacin and one for the acidic form. The two mature proteins show 76% homology at the nucleotide level, while the regions beyond the stop codons are 36% homologous. The differences in the content of aspartic acid accounts for the difference in net charge between the acidic and basic attacin. Further differences in charge can be obtained by post-translational removal of a lysine-containing tetrapeptide at the C-terminal end of the two proteins. Evidence for a prepro form of the basic attacin is presented.