MOLECULAR CHARACTERIZATION OF THE C-3 DNA PUFF GENE OF RHYNCHOSCIARA-AMERICANA

We have mapped a region of about 33 kb which includes the transcriptio n unit of the C-3 DNA puff gene of Rhynchosciara americana. The C-3 TU and a region extending approximately 800 bp upstream of the C-3 promo ter were characterized. The TU is composed of three exons and produces a 1.1-kb mRNA whose level in salivary glands increases with the expan sion of the C-3 puff. The C-3 messenger appears to undergo rapid deade nylation resulting in an RNA of about 0.95 kb which can still be obser ved in gland cells 15 h after the puff has regressed. The 1.1-kb mRNA codes for a 32.4-kDa, predominantly alpha-helical polypeptide with thr ee conserved parallel coiled-coil stretches. The aa composition and st ructure of this polypeptide suggests that it is secreted and contribut es to the formation of the cocoon in which the larvae pupate. The regi on upstream of the promoter contains several A-rich sequences with sim ilarity to the ACS of yeast which might have a role in the initiation of replication/amplification. (C) 1997 Elsevier Science B.V.