PROTEIN SYNTHESIS IN ESCHERICHIA COLI AFTER IRRADIATION WITH ULTRAVIOLET LIGHT

Post-irradiation protein and RNA synthesis were studied in Escherichia coli cells exposed to ultraviolet light doses ranging from 250 to 5000 erg/mm2. The following conclusions were drawn. (1) In u.v.-irradiated cells abnormal, shortened polypeptide chains are synthesized in addition to normal ones, presumably on shortened messenger RNA molecules which are reportedly produced when transcription is prematurely terminated at the site of u.v. lesions in DNA. (2) In u.v.-irradiated cells the number of polypeptide chains synthesized per unit time is also reduced, which is attributed to a reduced rate of messenger RNA synthesis. (3) The release of nascent proteins from polysomes is not greatly delayed in u.v.-irradiated cells, indicating that the termination of protein synthesis at the 3′-end of the messenger RNA molecule does not necessarily require a special termination sequence. (4) After u.v. irradiation, polysomes contain defective ribosomal subunits. © 1969.