tokens: It is now demonstrated that HIV-1 proviral latency in the monocytic cell line U1 , in which only extremely low levels of HIV-1 expression are detected in the baseline unstimulated state , is associated with alterations in nuclear factor-kappa B ( NF-kappa B ) moieties demonstrated in these cells by electrophoretic mobility shift assays ( EMSAs ) and in situ UV cross-linking studies .