Transfer RNAs in insect fat body during vitellogenin synthesis

Abstract

The biochemical characteristics of the fat body of adult virgin female Blaberus discoidalis were examined during the onset of vitellogenin synthesis. During the first 18-20 days following the final molt to the final form, approximately 110 mg of protein is accumulated in the ovaries of one insect, with half of that being deposited by day 10. Most of this protein is in the form of a 135,000 dalton complex which may be made up of an 85,000 dalton subunit and a mixture of subunits of different sizes. Despite this massive synthesis, measurements of total fat body RNA by the orcinol method following either of two different extraction methods indicated that at most a 1.6-fold increase in total RNA per DNA (measured by both diphenylamine and indole methods) occurs. The levels of tRNA('Gly), tRNA('Tyr), tRNA('Asp), and probably tRNA('Lys) were found to increase greatly, however, during the same time. RPC-5 chromatography of the isoacceptor distribution of these tRNAs showed that no new species appeared between 0 and 12 days, but that some changes in distribution occurred. There is one major isoacceptor for glycine and two for tyrosine, aspartate, and lysine. Small changes in isoacceptor distribution were seen in tRNA('Tyr) and tRNA('Lys), while tRNA('Asp) had a pronounced shift. This large shift was not mimicked in males, and was partially reversed in females which were not synthesizing vitellogenin. The isoacceptor which was decreased in proportion during vitellogenin synthesis was found to contain a glycosylated form of queuine, as demonstrated by its ability to bind to concanavalain in A-Sepharose. The relationship of this base change in tRNA('Asp) to the synthesis of vitellogenin in fat body was discussed.