Origins of two viral-like reverse transcriptases from milk particulates of lactating Chinese women

Two active forms of viral-type reverse transcriptase were present in milk particulates from Chinese women. These two enzymes differed with respect to molecular weight, elution position from poly(rC)-sepharose and preference for synthetic template poly(2'-O-methylcytidylate) oligo(dG) (poly(rCm) oligo(dG). Further investigations indicated that these two viral-type reverse transcriptases originated from different viral-like particles with separable buoyant densities in CsCl gradient. The larger enzyme (5.8S), which was eluted from a poly(rC)-sepharose column at 0.62-0.65 M KCl, was found in particles with density of 1.16 g/ml; the smaller enzyme (5S), which was eluted from poly(rC)-sepharose at 0.17-0.20 M KCl, was associated with particles having a density of 1.22 g/ml. Whether these human milk particles exhibit any structural similarity to the morphologies of known oncornaviruses will be further studied.