Two model developmental pathways are under investigation: 1. the head-assembly pathway of bacteriophage T4, and 2. the conidiation pathway of Aspergillus nidulans. T4 head assembly. Electrophoretic analysis of T4-infected cells has revealed two previously undetected phage coded proteins, pip and pZ. Both appear to be associated with the assembly core present in aberrant head-related structure and both are cleaved during phage assembly. The protein pZ* (the cleaved for of pZ), but not pip, is also present in mature phage particles. To determine whether these proteins are essential and, if so, at what stage of head assembly they function, we will seek mutants altered in or missing these proteins. Proteolytic cleavage of the pip protein during head assembly leaves one highly acidic peptide (internal peptide II) entrapped in the phage head. This peptide is highly variable both in charge and molecular weight among related T-even phage strains suggesting variable cleavage sites. Sequence studies on species variants of peptide II will continue with the aim of deducing the rules governing the cleavage of this fragment from its precursor. Conidiation in Aspergillus. Mutants temporally altered or blocked in conidiation will be studied to determine the structure of the control network for the genes expressed during asexual development. Ongoing studies will focus on: 1. specific changes in the specturm of protens during conidiation, 2. membrane changes during mycelial development, 3. a possible role of episomes in control of conidiation, and 4. isolation and analysis of mutants constitutive for conidial functions.