We have examined the effect of sodium butyrate, a potent inducer of differentiation in various cell systems, on the steady state RNA level and transcriptional activity of the c‐myc gene in Burkitt's lymphoma cells. Following sodium butyrate treatment a rapid decrease of c‐myc RNA was observed in all Burkitt's lymphoma cell lines studied, irrespective of the type of translocation, the location of the breakpoint relative to c‐myc or of the association with EBV. Since cellular genes induced by interferon are suspected to play a role in c‐myc regulation we have studied transcription of the 2‐5A synthetase gene in sodium butyrate‐treated Burkitt's lymphoma cells. Transcriptional activity and steady state mRNA levels of the 2‐5A synthetase gene were induced by sodium butyrate. The time course of induction excluded, however, that the decrease of c‐myc RNA is caused by induction of the 2‐5A synthetase/RNase L endonuclease system. The reduction of c‐myc RNA is caused, at least in part, by a reduced transcription rate, as shown by nuclear run‐on analysis. The fact that sodium butyrate is capable of downregulating a truncated c‐myc gene indicates that an important target site of transcriptional regulation is located outside the region encompassing the upstream regulatory sequences, the dual promoters and the leader region.

From human mycosis fungoides tumor-derived cell lines, Mycoplasma hyorhinis was isolated. This mycoplasma shared the following characteristics with retroviruses: uptake of 3H-uridine, but not of 3H-thymidine in cell culture; banding at 1.16 g/ml sucrose density and partial shift to retrovirus core density position (approximately equal to 1.24 g/ml) after detergent treatment; incorporation of 3H-TMP into high molecular weight material in standard reverse transcriptase assays with the template-primer poly (A) . (dT)12. On the other hand, the specific reverse transcriptase reaction of retroviruses with poly(A) . (dT)12 and poly(C) . (dG) approximately 16 was almost completely abolished in the presence of the mycoplasma. Thus, M. hyorhinis may interfere with identification and isolation procedures for retroviruses.

Distamycin A caused no significant inhibition of polyoma-virus growth or capsid and m RNA formation in embryonic mouse cells.