Transcription of 5 S RNA genes in vitro is feedback-inhibited by HeLa 5 S RNA.

Genes for xenopus oocyte-type 5 S ribosomal RNA are correctly transcribed in cell-free extracts derived from HeLa cells. At least two factors besides RNA polymerase III are required for the transcription process in somatic cells, one of which has affinity for DNA. The transcription of the oocyte-type 5 S genes can be selectively and completely repressed by purified HeLa 5 S RNA present in the transcription extract, while tRNA represses transcription incompletely and apparently nonspecifically. Weak competition of Xenopus 5 S ribosomal genes for a transcription factor(s) in the presence of HeLa 5 S RNA is discussed in terms of the relative strength of heterologous 5 S gene sequences to bind a transcription factor(s). Nonribosomal-bound 5 S RNA from the cytoplasm can be demonstrated to exist as a 7 S particle. The competition of 5 S RNA genes and 5 S RNA for a transcription factor and the finding of a 7 S particle in HeLa cells suggests a general feedback mechanism of 5 S RNA gene transcription.