Studies of microchromosomes and a G-C rich DNA satellite in the quail

The microchromosomes of Japanese quail fibroblasts are shown to be heterochromatic and nucleolus-organizing. Autoradiographic studies indicate that although some DNA replication takes place early, the time of intense replication is in the late S period after most replication in the macrochromosomes has ceased. Analytical centrifugation of quail DNA demonstrated a main band with a buoyant density of 1.701 g/cm³ and a satellite constituting about 5% of the DNA with a buoyant density of 1.715. The G-C content of the main and satellite band was 42 and 55 percent respecively by both buoyant density and DNA Tm. The satellite band renatured much more rapidly than main band DNA indicating it was composed of highly repetitive sequences. When purified satellite DNA was centrifuged at pH 13 it separated into three portions, a major central band constituting 72% of the satellite DNA, and two smaller bands, one heavier and one lighter than the central band, each constituting 14% of the satellite DNA. This indicated that in a portion of the satellite DNA the bases were non-randomly distributed in the half-DNA helices.Supported by N.I.H. Grant GM-15886, The Charles and Henrietta Detoy Research Fellowship.