Size of primary transcripts in Ehrlich ascites cells as measured by tetraphosphate determination.

Abstract
A method for the quantitation of 5''-tetraphosphate ends in 32P-labeled RNA was developed. The tetraphosphate content of different RNA fractions obtained from Ehrlich ascites cells labeled with 32P for different lengths of time was determined. Ribosomal RNA and poly(U)-binding RNA, labeled for long periods, (mRNA) lack 5''-terminal tetraphosphate. 5 S RNA, pulse labeled 4-5 S RNA, and poly(U)-binding hnRNA (heterogeneous nuclear RNA) do contain tetraphosphate. From the amount of the tetraphosphate, molecular weight data cna be calculated for these RNA fractions which agree with independent determinations by denaturing gel electrophoresis. The majority of the poly(A) containing hnRNA molecules are small (< 28 S) and contain the tetraphosphate of the primary transcript. Therefore, they do not originate from the 3''-end of large molecules by processing events.