Chromosomal proteins of Physarum polycephalum with preferential affinity for the sequence, poly d(A-T).poly d(A-T).

We have identified two novel chromosomal proteins from Physarum polycephalum using a protein blotting DNA-binding assay. A fraction of these proteins was readily released from nuclei by solutions of moderate ionic strength (0.15 N-0.35 M NaCl) or mild nuclease treatment and appear associated with chromatin that is nucleosome-free. A significant proportion of these proteins, however, was not released from nuclei by solutions of high ionic strength (1.6 M NaCl) or treatment with excess nuclease. These results suggest that these chromosomal proteins are distributed between transcriptionally-competent and inert domains of chromatin. Both proteins preferentially and tenaciously bound duplex DNA, especially to the alternating B-DNA conformation displayed by the synthetic sequence, poly d(A-T).poly d(A-T).