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The promoter region of the chicken aduh p-globin gene contains a sequence of 16 deoxyguanosine residues located at a nucleosome boundary in tissues where the gene is inactive. In definitive erythrocytes that express the p-globin gene, the nucleosome is displaced, the G-string and adjacent sequences are occupied by sequencespecific DNA-binding proteins, and a nuclease hypersensitive domain is generated in this region. To gain insight into the role of the G-string in this series of events, we have examined the proteins that bind to it. Using the gel mobility shift assay and a monoclonal antibody that blocks specific binding to the G-string, we have identified a specific protein, BGPl, that is found only in chicken erythroid cells and appears at the same time, or shortly before, the changes in chromatin structure. The antibody interacts strongly with BGPl and cross-reacts weakly with Spl. Although both BGPl and Spl require Zn^+ for their DNA-binding activity, these proteins differ in their binding-site specificities, chromatographic properties, and molecular weights. In contrast to Spl, which is found in a wide variety of cell types, BGPl is restricted to erythrocytes and is most abundant in definitive erythrocytes. Thus, its presence corresponds to the tissue-and stage-specific occupancy of the G-string in vivo.

The chicken beta A-globin gene contains in the neighborhood of its 5' promoter a (dG)-homopolymer sequence 16 base pairs long. The 66 kD protein BGP1 (beta globin protein 1), isolated from chicken erythrocytes, has been shown to bind specifically to this sequence. We describe further purification of BGP1, measure its affinity for the beta A-globin promoter binding site, and analyze its binding properties. The minimal binding sequence is seven dG residues; methylation interference studies show that each of these residues contacts BGP1. Binding competition experiments employing (dG).(dC) oligomers of varying lengths also consistent with (dG)7 as a minimum recognition sequence. All of the data can be explained by a model in which BGP1 binds to any contiguous set of seven (dG) residues, so that the effective constant for binding to (dG)n is proportional to n minus 6. This behavior may be typical of proteins that bind specifically to repeated sequences.

Basal rates of high-frequency vocalization by estrous female hamsters exceeded those typical of nonestrous females. Even higher rates of calling by estrous females were provoked by male odors (male shavings or anesthetized males). This suggests that cues which normally indicate a male's proximity can increase the rate of high-frequency calls by an estrous female. These findings are consistent with a view of female "ultrasounds" as sexual advertisements which indicate the locations, sexual receptivity, and relative passivity of estrous females to nearby male conspecifics. Male hamsters also produced ultrasounds at rates that seemed to depend on the availability of potential mates. Brief exposure to an awake female stimulated male calling; however, estrous females provoked higher call rates than did nonestrous females. Exposure to anesthetized females also increased the rate of male calling, which suggests that the stimulation of male calling by awake females depends in part on female odors. These results suggest that both male and female ultrasounds are parts of a communication system that facilitates reproduction by helping to coordinate social behavior with endocrine state.