Point mutations were introduced into the overlapping trans-regulatory genes (tat-III and trs) of human immunodeficiency virus type 1 (HIV-1), and the mutants were evaluated for virus expression. The results showed that tat-III has a positive transacting role and is required for transcriptional activation. A chain terminating mutation early in the trs gene resulted in an increase in transcription of viral messenger RNA as measured by nuclear transcription experiments, but only one major species of viral messenger RNA (1.8 kilobases) was detected, and little or no viral structural proteins were made. Thus, the trs gene product is essential for expression of virus structural proteins but, at the same time, may have a negative trans-regulatory role in transcription. Cotransfection of the point mutant proviruses defective in tat or trs with each other or with a complementary DNA clone containing tat and trs sequences restored the normal transcription pattern and subsequent virus production.