Developmentally regulated nonhistone proteins: evidence for deoxyribonucleic acid binding role and localization near deoxyribonuclease I sensitive domains of precartilage cell chromatin.

Differentiation of cartilage from precartilage mesenchyme in the chick embryo is accompanied by the loss of two abundant nonhistone proteins (Mr 35 500 and 125 000) termed PCP 35.5 and PCP 125. Here we examine the distribution of these and other developmentally regulated nonhistones in nuclease-sensitive regions of precartilage and cartilage chromatin. In particular, we show that PCP 35.5 is a tight DNA-binding protein that is localized near deoxyribonuclease I (DNase I) sensitive regions of precartilage chromatin. Localization of nonhistones was demonstrated by excising domains of precartilage chromatin with DNase II which are simultaneously highly enriched in PCP 35.5, in PCP 125, and DNase I sensitive DNA sequences. These domains comprise at least 25% of the cell's DNase I sensitive sequences, as well as small DNase I resistant regions with which the two nonhistones are associated. These findings suggest that PCP 35.5 (and possibly PCP 125) may play a developmentally regulated role nearby DNase I sensitive domains of the cartilage progenitor cell chromatin.