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Structures and expression of mRNAs coding for major plasma proteins of Bombyx mori
Abstract:
A group of structurally related proteins, referred to as '30K proteins', accumulate in a stage-dependent fashion in the larval hemolymph of the silkworm, Bombyx mori. To investigate the regulatory mechanisms of the 30K protein biosynthesis in the fat body, mRNA sequences coding for these plasma proteins were cloned and their structures and expression during the larval development were studied. Five plasmid clones, each bearing a distinct mRNA sequence coding for the 30K protein component, were isolated from a cDNA library constructed from the fat body poly(A)RNA of the mid-fifth instar larvae. These clones were remarkably similar to each other with respect to both the nucleotide and the amino-acid sequences. Each clone carried an open reading frame for amino-acid residues 251 to 264, with a typical signal sequence for transmembrane secretion at the deduced amino-terminal domain. Northern blot hybridization provided evidence that the developmental change in the amount of 30K protein mRNAs in the fat body reflects well that of the hemolymph concentration of 30K proteins, indicating that the biosynthesis of 30K proteins is developmentally regulated at a transcriptional or post-transcriptional level in the fat body.
Insights
Researchers studied the biosynthesis of Bombyx mori 30K proteins, finding that their production in the fat body is developmentally regulated. This regulation occurs at transcriptional or post-transcriptional levels, influencing hemolymph protein concentration.
Area of Science:
- Biochemistry
- Molecular Biology
- Entomology
Background:
- Bombyx mori larvae exhibit stage-dependent accumulation of structurally related '30K proteins' in their hemolymph.
- Understanding the regulation of 30K protein biosynthesis is crucial for insect physiology research.
Purpose of the Study:
- To investigate the regulatory mechanisms governing 30K protein biosynthesis in the silkworm fat body.
- To clone and characterize mRNA sequences encoding 30K proteins and analyze their expression during larval development.
Main Methods:
- Construction of a cDNA library from Bombyx mori fat body poly(A)RNA.
- Isolation and sequencing of five distinct plasmid clones encoding 30K protein components.
- Northern blot hybridization to analyze mRNA expression levels in the fat body.
Main Results:
- Five highly similar mRNA sequences coding for 30K proteins were isolated, sharing nucleotide and amino acid similarities.
- Each clone contained an open reading frame with a signal sequence, suggesting transmembrane secretion.
- Fat body mRNA levels of 30K proteins correlated with hemolymph protein concentrations during larval development.
Conclusions:
- 30K protein biosynthesis in Bombyx mori is developmentally regulated at the transcriptional or post-transcriptional level within the fat body.
- The findings provide insights into the molecular mechanisms controlling plasma protein production in insects.
- This study establishes a foundation for further research into insect hemolymph protein regulation.