Existence and expression of tumor virus genes in chick embryo cells

Abstract

A majority of chick embryo cells have previously been shown to contain a genetic element called chick-cell associated helper factor that is responsible for the presence of the helper function for the formation of an infectious form of the Bryan strain of Rous sarcoma virus. The helper factor was unable to mature into complete virus by itself, but, with the assistance of other leukosis viruses, its genome was recovered as a new Rous-associated virus-60. The present study demonstrated a good correlation between high levels of helper function and production of a group specific antigen to avian tumor viruses. Among the minority of embryos lacking detectable amounts of the antigen, about 40% possessed the helper function at low levels. By the use of a sensitive method, Rous associated virus-60 could also be recovered from chick embryo cells that are negative for the group-specific antigen. It is suggested that all chick embryos contain the genetic information for the helper factor; its expression is controlled by a regulatory gene.