Jnanankur Bag

Cytoplasmic nonpolysomal ribonucleoprotein complexes and translational control

SummaryIn this article, we discuss our attempts to establish the existence in the cytoplasm of regulatory molecules involved in translational control. Our studies have revealed the presence of cAMP independent protein kinase in the free mRNP complex capable of phosphorylating a Mr = 38 000 polypeptide, also part of the same complex. Both the kinase and the acceptor protein were found also as free proteins in the cytoplasmic pool. This kinase has been shown to be distinct from the heme regulated enzyme that phosphorylates the small subunit of eIF-2.Other regulatory molecules include small molecular weight RNAs found as part of an RNP complex. A 4S fraction isolated from this complex inhibited the translation of both capped and uncapped mRNAs in a cell-free protein synthesizing system.The biological role of the protein kinase and the 4S RNA fraction is considered.

Low Mr RNAs of chicken muscle cells and their interaction with messenger and ribosomal RNAs

Control of gene expression at the post-transcriptional level has generated considerable attention [ 11. Whether regulation of mRNA translation in eukaryotic cells is a significant factor in this process, has been tested by different systems [ 1,2]. We have revealed a low-M, 4.4 S RNA in a ribonucleoprotein fraction capable of interfering with protein synthesis [3]. This low-M, RNA inhibited translation of both capped and uncapped mRNAs and appeared to act at a stage early in the translation process [3]. This study was designed to determine whether this inhibitory RNA acts by interacting with complementary sequence in mRNA. The data obtained indicate that a low-M,, RNA comigrating with bulk tRNA hybridizes to both polysomal and free cytoplasmic mRNAs. trifugation at 100 000 x g for 1 h. The post-polysomal supernatant was further centrifuged in a 75 Ti rotor at 40000 rev./min for 16 h to pellet post-polysomal ribonucleoprotein complexes [3]. To isolate RNA, the pellet was suspended in 10 mM sodium-acetate, 100 mM NaCl, 1% SDS (pH 5.0) buffer to give 5 A260 unit/ml and extracted with a mixture of phenol:chloroform (1: 1) as in [3].