A fundamental principle of many developing systems is the mutually exclusive nature of cell growth and cellular differentiation. Dictyostelium discoideum provides a model for investigating this reciprocal relationship in that in the vegetative state the amoebae have an unlimited capacity for self renewal through growth and mitotic divisions while initiation of the developmental program results in a cessation of growth and division and leads to cellular differentiation. During the past granting period, the regulatory mechanisms underlying the switch from growth to development have been investigated primarily be examining the resulting differential expression of a variety of genes. It is proposed to continue this approach by investigating the molecular mechanisms bringing about the deactivation of transcription of one of these genes, V4, in response to cessation of growth and activation of the developmental program. This will be done by examining the protein factors involved in the expression of the V4 gene, and how the activity of these factors is coupled to the transition from growth to development. V4 gene expression is highly sensitive to levels and types of nutrients present in the environment. In addition, the encoded product of the V4 gene has been shown to be required for the transition from growth to development, and it is involved in the deactivation of expression of all growth specific genes examined and in the induction of expression of most "early developmental specific" genes. The role of this gene product in bringing about a cessation of growth and in initiating the developmental program and how it is involved in regulating the expression of the above mentioned genes will be examined. This will require production and purification of the encoded protein, examining any activity associated with it, and determining its cellular location, its modification state(s), and identifying other proteins which may interact with it. The possible interplay between the V4 gene product and several other factors postulated to be involved in the early regulatory events of the developmental program will be investigated.
