Identification and molecular analysis of a multigene family encoding calliphorin, the major larval serum protein of Calliphora vicina

A library of Calliphora vicina genomic DNA was constructed in the λEMBL3 vector and screened for recombinant phages containing chromosomal segments encoding calliphorin, the major larval serum protein (LSP) of Calliphora. A large series of recombinants hybridizing with in vitro labelled poly(A)⁺ RNA from Calliphora larval fat bodies and with specific probes derived from the LSP-1 genes of Drosophila melanogaster was isolated. Five of these phages, chosen at random, were shown by hybrid selection to retain calliphorin mRNA specifically. Eleven calliphorin mRNA-homologous regions were located on restriction maps of these phages by hybridization with 5' end-labelled poly(A)⁺ RNA from Calliphora larval fat bodies. Each phage contains at least two calliphorin genes arranged in direct repeat orientation and seperated by 3.5–5 kb intergenic regions. The genes display similar but not identical restriction patterns. Filter hybridization and heteroduplex analysis indicate that they share a detectable homology with the LSP-1β gene of D. melanogaster. Whole genome Southern analysis showed that these genes belong to a large family of closely related calliphorin genes which were found by in situ hybridization to polytene chromosomes of trichogen cells to be clustered in region 4a of chromosome 2 of Calliphora vicina.