Interactions between Tat and TAR and human immunodeficiency virus replication are facilitated by human cyclin T1 but not cyclins T2a or T2b

The transcriptional transactivator (Tat) from the human immunodeficiency vi rus (HIV) does not function efficiently in Chinese hamster ovary (CHO) cell s. Only somatic cell hybrids between CHO and human cells and CHO cells cont aining human chromosome 12 (CHO12) support high levels of Tat transactivati on. This restriction was mapped to interactions between Tat and TAR. Recent ly, human cyclin T1 was found to increase the binding of Tat to TAR and lev els of Tat transactivation in rodent cells. By combining individually with CDK9, cyclin T1 or related cyclins T2a and T2b form distinct positive trans cription elongation factor b (P-TEFb) complexes. In this report, we found t hat of these three cyclins, only cyclin T1 is encoded on human chromosome 1 2 and is responsible for its effects in CHO cells. Moreover, only human cyc lin T1, not mouse cyclin T1 or human cyclins T2a or T2b, supported interact ions between Tat and TAR in vitro. Finally after introducing appropriate re ceptors and human cyclin T1 into CHO cells, they became permissive for infe ction by and replication of HIV. (C) 1999 Academic Press.