ИСТИНА

The Ku protein plays a key role in the DNA double-strand break repair by non-homologous end-joining mechanism. In addition, it participates in transcription, telomere maintenance, V(D)J-recombination and some other processes. Ku is a participant human immunodeficiency virus-1 (HIV-1) replication at the stages of integration and transcription although the exact mechanism of Ku-dependent transcriptional regulation is unclear. We identified RNA structural motifs important for the interaction with Ku. The highest Ku affinity was detected toward a hairpin RNA structure containing bulk bulge close to the loop. TAR RNA forms a hairpin at the 5’-end of HIV mRNA and has a Ku preferred structure. TAR RNA lacking the bulge had a significantly lower affinity towards Ku. We constructed a set of reporter vectors containing firefly luciferase gene either under the control of wild-type HIV LTR or its deletion mutants: lacking the region coding for the whole TAR RNA or the region corresponding to the bulge of TAR RNA. CRISPR/Cas9 depletion of Ku led to a significant decrease in luciferase expression from HIV LTR and only slightly influenced the mutant constructs. Overexpression of Ku protein in Ku-knockdown cells partially restored luciferase expression from WT LTR. TNF-a mediated induction of HIV transcription initiation had no significant impact on Ku-dependent regulation. Tat is an HIV trans-activating protein participating in activation of transcription elongation that binds to TAR RNA and recruits P-TEFbcomplex to the promoter for the phosphorylation of RNAP II. Ku overexpression reduced Tat-mediated activation of elongation and Ku depletion increased the effect of Tat protein. Moreover, the effect of Ku depletion on transcription from LTR promoter was abolished by Tat expression. These data demonstrate the role of TAR RNA in the positive regulation of transcriptional elongation from LTR promoter by Ku.