Interruption of T-cell signal transduction by lentivirus lytic peptides from HIV-1 transmembrane protein.

Two peptide segments designated LLP1 (residues 828-855) and LLP2 (residues 768-788) of the HIV-1 transmembrane (TM) envelope protein display structural and functional properties of calmodulin (CaM) binding. These LLP segments may contribute to cytopathogenesis by binding cellular CaM and inhibiting normal CaM-regulated signal transduction pathways. To determine whether these peptides could interrupt signal transduction in vivo, a cellular assay which uses a reporter gene linked to the nuclear factor of activated T cells (NF-AT) was used. Signal transduction perturbation was tested by exogenous addition of LLPs, W-7 or ionomycin; the LLPs inhibited NF-AT-mediated signal transduction as measured by reduced reporter activity. The LLP inhibition profile of NF-AT-driven luciferase activity was similar to the CaM inhibitor W-7. This was in direct contrast to ionomycin, a mobile calcium ion carrier which caused a significant increase in luciferase activity. These findings are consistent with the hypothesis that the CaM-binding properties of TM may contribute to defects in signal transduction leading to the T-cell anergy observed in patients infected with HIV-1.

Evidence of participation of McrB(S) in McrBC restriction in Escherichia coli K-12.

The McrBC restriction system has the ability to restrict DNA containing 5-hydroxymethylcytosine, N4-methylcytosine, and 5-methylcytosine at specific sequences. The mcrB gene produces two gene products. The complete mcrB open reading frame produces a 51-kDa protein (McrB(L)) and a 33-kDa protein (McrB(S)). The smaller McrB polypeptide is produced from an in-frame, internal translational start site in the mcrB gene. The McrB(S) sequence is identical to that of McrB(L) except that it lacks 161 amino acids present at the N-terminal end of the latter protein. It has been suggested that McrB(L) is the DNA binding restriction subunit. The function of McrB(S) is unknown, although there has been speculation that it plays some role in the modulation of McrBC restriction. Studies of the function of McrB(S) have been challenging since it is produced in frame with McrB(L). In this study, we tested the effects of underproduction (via antisense RNA) and overproduction (via gene dosage) of mcrBC gene products on restriction levels of the mcrBC+ strain JM107. Among the parameters monitored was the induction of SOS responses, which indicate of DNA damage. Evidence from this study suggests that McrB(S) is necessary for stabilization of the McrBC restriction complex in vivo.