Transcribed Oligonucleotide Sequences in Hela Cell hnRNA and mRNA

Abstract

This chapter reviews that the poly (A) sequences at the 3' ends of many of the hnRNA molecules of animal cell nuclei provided the first evidence for the existence of common sequences within this highly heterogeneous RNA population. Additional sequence homologies were revealed when high concentrations of two shorter single-base sequences were found in the hnRNA of HeLa cells. One is an internal sequence of about 25 AMPS that, in contrast to the longer poly (A) at the 3' end, is transcribed. The other is a poly (U) sequence of 30–40 nucleotides concentrated in the largest hnRNA molecules in regions distant from the poly (A) terminus. The chapter examines the properties and distribution of these sequences in the nucleus and cytoplasm of HeLa cells in the expectation that insights can be gained on mechanisms of mRNA production through hnRNA processing. It reviews that poly (A) preparations from ribonuclease digests of hnRNA purified on oligo (dT) -cellulose contain a small AMP-rich component that readily separates from the large poly (A) sequence during electrophoresis. It was concluded that, unlike large poly (A), this small AMP-rich species is riot at the 3' end of hnRNA molecules.