4.5S RNA is a group of RNAs 90 to 94
nucleotides long (length polymorphism due to a varying number of
UMP residues at the 3' end) that form hydrogen bonds with
poly(A)-terminated RNAs isolated from mouse, hamster, or rat cells (W. R. Jelinek and L. Leinwand, Cell 15:205-214, 1978; F. Harada, N. Kato, and H.-O. Hoshino,
Nucleic Acids Res. 7:909-917, 1979). We have cloned a gene that encodes the
4.5S RNA. It is repeated 850 (sigma = 54) times per haploid mouse genome and 690 (sigma = 59) times per haploid rat genome. Most, if not all, of the repeats in both species are arrayed in tandem. The repeat unit is 4,245 base pairs long in mouse
DNA (the complete base sequence of one repeat unit is presented) and approximately 5,300 base pairs in rat
DNA. This accounts for approximately 3 X 10(6) base pairs of genomic
DNA in each species, or 0.1% of the genome. Cultured murine
erythroleukemia cells contain 13,000 molecules per cell of the
4.5S RNA, which can be labeled to equilibrium in 90 min by [3H]
uridine added to the culture medium. The
4.5S RNA, therefore, has a short half-life. The
4.5S RNA can be cross-linked in vivo by
4'-aminomethyl-4,5',8-trimethylpsoralen to murine
erythroleukemia cell
poly(A)-terminated cytoplasmic
RNA contained in
ribonucleoprotein particles.