Viral MIP-I (also termed vMIP-1 alpha) cDNA encodes a 95 amino acid (aa) residue precursor protein with a 24 aa residue signal peptide that is cleaved to yield a 71 aa residue mature protein. Among human chemokines, vMIP-I is most closely related to MIP-1 alpha, sharing approximately 38% amino acid sequence identity. At the amino acid sequence level, vMIP-I and vMIP-II also share 48% identity. vMIP-I and vMIP-II are more closely related to one another phylogenetically than to other human chemokines, suggesting that they may have arisen by gene duplication within the virus rather than by two independent gene aquisitions. Both vMIP-I and vMIP-II have been shown to partially block HIV infection of peripheral blood mononuclear cells. vMIP-I and vMIP-II have also been found to be highly angiogenic in the chorioallantoic assay, suggesting that they may be partially responsible for the marked vascularity seen in KSHV-associated tumors.