Further evidence for oncornaviruses in human milk: the production of cores.

Cores, or nucleoids, have been isolated from particles in human milk. The cores have a density of 1.26-1.27 g/ml and contain a 60-70S RNA in association with an RNA-instructed DNA polymerase. The data offer further evidence of similarity between human milk particles and animal RNA tumor viruses. In addition, core isolation provides a new method for detection of these particles by minimizing the difficulties generated by the presence of cell-associated debris often found in the density region (1.16-1.19 g/ml) characteristic of the intact virion. The procedures described now make available preparations of purified subviral components of a putative human RNA tumor virus.