An evolutionary conserved Hexim1 peptide binds to the Cdk9 catalytic site to inhibit P-TEFb.

The positive transcription elongation factor (P-TEFb) is required for the transcription of most genes by RNA polymerase II. Hexim proteins associated with 7SK RNA bind to P-TEFb and reversibly inhibit its activity. P-TEFb comprises the Cdk9 cyclin-dependent kinase and a cyclin T.

Association of human mitochondrial lysyl-tRNA synthetase with HIV-1 GagPol does not require other viral proteins.

In human, the cytoplasmic (cLysRS) and mitochondrial (mLysRS) species of lysyl-tRNA synthetase are encoded by a single gene. Following HIV-1 infection, mLysRS is selectively taken up into viral particles along with the three tRNA isoacceptors. The GagPol polyprotein precursor is involved in this process.

A Cyclin T1 point mutation that abolishes positive transcription elongation factor (P-TEFb) binding to Hexim1 and HIV tat.

Background: The positive transcription elongation factor b (P-TEFb) plays an essential role in activating HIV genome transcription. It is recruited to the HIV LTR promoter through an interaction between the Tat viral protein and its Cyclin T1 subunit. P-TEFb activity is inhibited by direct binding of its subunit Cyclin T (1 or 2) with Hexim (1 or 2), a cellular protein, bound to the 7SK small nuclear RNA.

Activation of human mitochondrial lysyl-tRNA synthetase upon maturation of its premitochondrial precursor.

The cytoplasmic and mitochondrial species of human lysyl-tRNA synthetase are encoded by a single gene by means of alternative splicing of the KARS1 gene. The cytosolic enzyme possesses a eukaryote-specific N-terminal polypeptide extension that confers on the native enzyme potent tRNA binding properties required for the vectorial transfer of tRNA from the synthetase to elongation factor EF1A within the eukaryotic translation machinery. The mitochondrial enzyme matures from its precursor upon being targeted to that organelle.

Association of mitochondrial Lysyl-tRNA synthetase with HIV-1 GagPol involves catalytic domain of the synthetase and transframe and integrase domains of Pol.

Cytosolic and mitochondrial lysyl-tRNA synthetases (LysRS) are encoded by a single gene and can be distinguished only according to their very N-terminal sequences. It was believed that cytosolic LysRS is packaged into HIV-1 virions via its association with Gag. Using monospecific antibodies, it was later shown that only the mitochondrial LysRS is taken up in viral particles along with tRNA(3)(Lys), the primer for reverse transcription of the HIV-1 genome.