Abstract
Introduction. The study of the molecular biology of retroviruses has revealed a number of features not found in other groups of viruses. In recent years, a large number of excellent reviews of the field have appeared (Table 1). In writing this article, it is not my intention to cover ground already well treated in review form. Instead, I will consider only a limited number of interrelated subjects dealing with the organization of information in tumour virus genomes and its transfer from parent to progeny. In general, I will ignore primary data and present only the inferred structures and mechanisms and point out experimental approaches that might fill in gaps in our knowledge.
Retroviruses form a large and diverse group, with isolates from many different vertebrates. In most cases, our knowledge of the molecular biology of the viruses is derived from one model system, the avian sarcoma-leukosis viruses (ASV).