Sequence analysis and expression of Met-rich storage protein SP-1 of Hyphantria cunea

We isolated and sequenced a cDNA clone corresponding to the 2.5 kb storage protein (SP-1) from fall webworm, Hyphantria cunea. The SP-1 gene encoded a pre-protein of 753 amino acids, including a signal peptide of 15 amino acids. The deduced amino acid sequence of SP-1 contained one potential N-glycosylation site, and the calculated isoelectric point and molecular weight of secreted SP-1 were pI = 8.38 and 86.8 kDa, respectively. A Northern blot of mRNA from various developmental stages revealed that the SP-1 mRNA in fat body appears in early last instar larvae and accumulates to a maximum level at the end of last instar larvae. The persistence of SP-1 transcript through the early pupal stage suggests that its mRNA might be stable or expressed during the pupal stage. SP-1 transcription was also found in the ovary as well as testis. This local expression of SP-1 in both reproductive organs seems to allow the insect to keep its reproductive activity under a nutritional stress.