Inter-specific sequence conservation and intra-individual sequence variation in a spider silk gene.

Currently, studies on major ampullate spidroin 1 (MaSp1) genes of non-orb weaving spiders are few, and it is not clear whether genes of these organisms exhibit the same characteristics as those of orb-weavers. In addition, many studies have proposed that MaSp1 might be a single gene with allelic variants, but supporting evidence is still lacking. In this study, we compared partial DNA and amino acid sequences of MaSp1 cloned from different spider guilds. We also cloned partial MaSp1 sequences from genomic DNA and cDNA of the same individuals of spiders using the same primer combination to see if different molecular forms existed. In the repetitive region of partial MaSp1 sequences obtained, GGX, GA and poly-A motifs were present in all Araneomorphae and Mygalomorpae species examined. An extreme similarity in MaSp1 non-repetitive portions was found in sequences of ecribellate, cribellate and Mygalomorphae web-builders and such a result suggested that this sequence might exhibit an important function. A comparison of sequences amplified from the same individual showed that substitutions in amino acids occurred in both repetitive and non-repetitive regions, with a much higher variation in the former. These results suggest that the MaSp1 of Araneomorphae spiders exhibits several forms in an individual spider and it might be either a multiple gene or a single gene with a multiple exon/intron organization.