SILK GLAND SPECIFIC CDNAS FROM GALLERIA-MELLONELLA L

Four classes of Galleria mellonella silk gland specific cDNAs, designated PG-1, PG-2, MG-1 and MG-2, were cloned, sequenced and used as probes in Northern and Southern blots. Analysis of the results and their comparison with the data available for Bombyx mori reveal that the isolated cDNAs correspond to mRNAs for major silk proteins. Two small transcripts (1.1 and 1.2 kb), detected with PG-1 in the posterior region of Galleria silk glands, represent mRNAs for small proteins related to the light chain fibroin of Bombyx. A large transcript (greater-than-or-equal-to 10 kb) homologous to PG-2 seems to be the mRNA for the heavy chain fibroin. Conceptual translation of available PG-2 sequence yields a product with similar amino acid composition as reported for the chemically analyzed fibroin. Hybridization to Southern blots of Galleria genomic DNA showed that PG-1 and PG-2 correspond to separate genes. In the middle silk gland region, multiple transcripts homologous to MG-1 are produced. They include 1.9 and 4.2 kb species, and in certain developmental periods also 3.2, 7.2 and greater-than-or-equal-to 10 kb products. Two different transcripts, one dominant (3.4 kb) and one rare (5.2 kb) were revealed with the MG-2 probe. MG-1 and MG-2 cDNAs contain somewhat similar repeats, and their deduced translation products resemble Bomhyx sericins by the dominance of serine and the high content of glycine and asparagine. Southern blots indicated that MG-1 and MG-2 represent different sericin genes apparently corresponding to Ser-1 and Ser-2 genes of Bombyx.