The effects of HIV-1 encoded proteins NCp7, vpr and NCp7:vpr complex o
n the activity of protein phosphatase-2A(0) have been tested, We repor
t that NCp7 is an activator of protein phosphatase-2A(0) and that vpr
activated protein phosphatase-2A(0) only slightly, We also report that
NCp7 and vpr form a tight complex which becomes a more potent activat
or of protein phosphatase-2A(0) than NCp7 alone, The ability of NCp7 t
o activate protein phosphatase-2A(0) is regulated by vpr. The C-termin
al portion of vpr prevents NCp7 from activating protein phosphatase-2A
(0) while the N-terminal portion of vpr potentiates the effect of NCp7
on the activity of protein phosphatase-2A(0), Our findings indicate t
hat vpr may be acting as a targeting subunit which directs NCp7 to act
ivate protein phosphatase-2A(0), In view of the fact that protein phos
phatase-2A functions as an inhibitor of G(0) to M transition of the ce
ll cycle and is involved in other key cellular processes such as the c
ontrol of RNA transcription, the results presented in this report may
explain how HIV-1 causes cell cycle arrest which may lead to CD4+ T ce
ll depletion and also how it disturbs normal cellular processes of its
host cell.