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RNA polymerases and transcriptional activity of the fat body during the final larval instar of the tobacco hornworm Manduca sexta
Author(s) -
Sridhara S.
Publication year - 1995
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/arch.940300204
Subject(s) - biology , rna , polymerase , rna polymerase i , manduca sexta , rna polymerase , small nuclear rna , microbiology and biotechnology , biochemistry , rna polymerase ii , rna editing , rna dependent rna polymerase , rna polymerase iii , enzyme , gene expression , gene , larva , promoter , botany
The activities of RNA polymerases I and II in the fat body of the tobacco hornworm larva increased during feeding and then declined during wandering in the fifth instar (Sridhara and Gilbert, Dev Biol 45:7–21 [1975]). RNA polymerase II activity was much higher than that of RNA polymerase I. To determine how the differences in the activities of the two enzymes and their developmental changes correlate with changes in RNA and protein, the contents of these macromolecules were determined during the same period. RNA and protein increased by about 8 to 10‐fold during the feeding period. Activities of RNA polymerases I and II in nuclei, as well as those present in “free” (not transcribing) and “engaged” (transcribing) pools, were measured. Incorporation of labeled uridine into RNA by fat body cells in vitro was correlated to nuclear enzyme activities. The amounts of RNA polymerases I, II, and III were determined by the application of an ELISA with subunit‐specific monoclonal antibodies. Results showed that even though the in vitro activity of RNA polymerase II and its amounts are higher than those of RNA polymerase I and III, rRNA and tRNA syntheses predominated over mRNA synthesis in vivo. The activities and amounts of RNA polymerase II in the “free” pool were higher than those for RNA polymerase I. The “free” pools of the two enzymes increased as the larva progressed through the fifth instar. There appears to be little correlation between RNA polymerase activities and RNA synthesis during wandering, as RNA synthesis by the tissue and nuclear RNA polymerase activities declined faster than the amounts of the enzymes. The amount of RNA remained fairly steady during the same period. 20‐hydroxyecdysone did not affect either the RNA polymerase activities or RNA synthesis of the fat body cultured in vitro. © 1995 Wiley‐Liss, Inc.