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Structures and organization of major plasma protein genes of the silkworm Bombyx mori
Abstract:
In the silkworm, Bombyx mori, a group of structurally related proteins, termed 30K proteins, accumulate in the hemolymph of the last instar larvae. We have isolated and characterized three genes, each of which encodes a distinct 30K protein component. Each 30K protein gene is composed of a short first exon and a protein-coding second exon interspersed by a single intron. The transcription initiation site of the 30K protein mRNA was identified at the nucleotide level. A typical TATA box exists some 30 base-pairs upstream from the transcription initiation site. The 5'-flanking region of each gene also contains octamer-like sequences. Restriction mapping analyses revealed that the cloned 46 x 10(3) base-pair region of the chromosomal DNA bears three 30K protein genes. Several copies of highly reiterated retrotransposon-like sequences are present around the 30K protein genes. S1 nuclease protection analysis provided evidence that the biosynthesis of 30K protein is regulated in a stage-specific manner at the transcriptional level in the fat body.
Insights
Researchers identified three genes encoding silkworm 30K proteins. Their expression is stage-specifically regulated at the transcriptional level in the fat body during larval development.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Silkworm (Bombyx mori) larvae accumulate structurally related 30K proteins in hemolymph.
- These proteins play a role in larval development.
Purpose of the Study:
- To isolate and characterize the genes encoding Bombyx mori 30K proteins.
- To investigate the transcriptional regulation of 30K protein biosynthesis.
Main Methods:
- Gene isolation and characterization.
- Nucleotide sequence analysis of gene structure and 5'-flanking regions.
- Restriction mapping of chromosomal DNA.
- S1 nuclease protection assays to determine transcriptional regulation.
Main Results:
- Three distinct genes encoding 30K protein components were isolated and characterized.
- Each gene features a short first exon, a protein-coding second exon, and a single intron.
- Promoter elements including a TATA box and octamer-like sequences were identified in the 5'-flanking regions.
- The three 30K protein genes are located within a 46 kb region of chromosomal DNA, interspersed with retrotransposon-like sequences.
- 30K protein biosynthesis is regulated at the transcriptional level in a stage-specific manner in the fat body.
Conclusions:
- The study successfully identified and characterized the genes responsible for 30K protein production in Bombyx mori.
- Transcriptional regulation in the fat body is the primary mechanism controlling the stage-specific expression of these genes during larval development.