Abstract
Small circular DNAs ranging in contour length from 0.06 to 3.5 micrometers have been isolated from bursas of 19-day chicken embryos and 4- to 5-week-old chickens. Small circular DNA is present in bursas of 19-day embryos at approximately 0.2 molecules per cell and is very heterogeneous, lacking distinct size classes; most molecules have contour lengths of less than 0.04 micrometers. In contrast, small circular DNA is present in bursas of 4- to 5-week old chickens at about 4 molecules per cell, and although this DNA is still heterogeneous, it contains a major distinct class of molecules 0.8 micrometers in size. These small circular DNAs may be products of developmental gene rearrangements occurring in the chromosomal DNA of lymphocytes in the bursa.