EVOLUTION OF THE LARVAL CUTICLE PROTEINS CODED BY THE SECONDARY SEX-CHROMOSOME PAIR - X2 AND NEO-Y OF DROSOPHILA-MIRANDA .2. COMPARISON AT THE AMINO-ACID-SEQUENCE LEVEL

The larval cuticle proteins (LCPs) are encoded by a multigene family, Lcp1-4, located at the right arm of the metacentric autosome 2 (2R) in Drosophila melanogaster. Due to a chromosome fusion the Lcp locus of Drosophila miranda is situated on a pair of secondary sex chromosomes, the X2 and neo-Y chromosomes. Comparing the deduced amino acid sequen ces of the autosomal D. melanogaster loci with the sex-chromosomal loc i of D. miranda, we were able to trace the evolution of the Lcp loci w ith respect to their different chromosomal inheritance. The length of the signal peptide is conserved in all four LCPs, while the size of th e mature LCPs varies. Conserved protein motifs became obvious from the alignment, indicating regions of structural and functional importance . Analyzing intra- and interspecific sequence similarities of the Lcp gene families allowed us to reconstruct the phylogeny of the gene clus ter. Alignment with cuticle amino acid sequences originating from dive rgent insect species reveals motifs already present in the primordial insect LCPs. These motifs indicate different levels of constraint acti ng during the evolution of the LCPs.