The focus of research in the Laboratory of Molecular Growth Regulation is on control of cell proliferation in mammalian cells. Of particular interest are interrelationships between growth control and basic processes such as cellular differentiation and aging. Using recently developed gene transfer technology in conjunction with the standard array of recombinant DNA methodologies, several related questions are being investigated: i) What are the molecular mechanisms that control cellular senescence in normal human cells? ii) Why do rodent cells become immortalized at a far higher frequency than human or other primate cells? iii) What roles do cellular anti-oncogenes encoding p53 and retinoblastoma gene products have in cellular quiescence and senescence? and iv) Do interspersed repetitive sequences, which comprise 5-10% or more of mammalian genomes, represent unconventional but fundamentally important elements in the control of differentiation, tumor suppression and cellular senescence.