Identification of a developmentally regulated gene for a 140-kDa secretory protein in salivary glands of Chironomus tentans larvae.
Secretory proteins are synthesized in salivary glands of the insect, Chironomus tentans, and assemble in vivo into silk-like threads which aquatic larvae use to construct tubes for filter feeding and pupation. Thus far, all known secretory protein genes contain repetitious protein-coding sequences and are located in cytological structures known as Balbiani rings, giant puffs found on polytene secretory cell chromosomes. In this paper we describe the identification of another secretory protein gene which is comprised of repeated sequences; however, this gene is not located in a Balbiani ring. Two partial cDNA clones from a 3.6-kilobase pair poly(A)+ RNA were sequenced and found to contain two open reading frames for protein synthesis. Antibodies were raised against synthetic oligopeptides whose sequences were derived from these two open reading frames. An immunoaffinity-purified antibody for one of these peptides bound specifically to a 140-kDa secretory protein (sp140). The cDNA sequences contain tandem repeats of 42 base pairs which encode a repeat of 14 amino acids with a composition and oligopeptide sequence similar to other secretory proteins. The C. tentans genome contains about 70 copies of this 42-base pair repeat organized as a contiguous block of 3 kilobase pairs or less. The sp140 gene was mapped by in situ hybridization to polytene chromosome band I-17-B. Developmental studies of protein accumulation, steady-state levels of mRNA, and relative transcription rate suggested that the sp140 gene is developmentally regulated so that maximal expression is achieved during the prepupal stages of the fourth larval instar. Based upon these results we proposed that sp140 gene belongs to a prepupal class of secretory protein genes. While the sp140 gene shares structural and expression characteristics with other secretory protein genes, its unique chromosomal location shows that this multigene family is not restricted to Balbiani rings.
Dignam
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Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216-4505.
Yang
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Lezzi
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Case
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002683:Chironomidae / Q000235:genetics* / Q000254:growth & development; D003001:Cloning, Molecular; D004247:DNA / Q000302:isolation & purification; D004175:Diptera / Q000235:genetics*; D005786:Gene Expression Regulation; D005796:Genes; D007814:Larva / Q000254:growth & development; D008969:Molecular Sequence Data; D008970:Molecular Weight; D012313:RNA / Q000302:isolation & purification; D012091:Repetitive Sequences, Nucleic Acid; D012471:Salivary Proteins and Peptides / Q000235:genetics* / Q000302:isolation & purification / Q000502:physiology; D014158:Transcription, Genetic
D012471:Salivary Proteins and Peptides; D012313:RNA; D004247:DNA