Evolutionary sequence divergence within repeated DNA families of higher plant genomes

The higher proportion of repeated DNA sequences in the garden pea (Pisum sativum) than in the mung bean (Vigna radiata), as well as other differences between these legume genomes, are consistent with a higher rate of sequence amplification in the former. This hypothesis leads to a prediction that repeated sequence families inPisum are mostly heterogeneous, as defined by Bendich and Anderson (1977), whileVigna families are homogeneous. An assay developed by these authors to distinguish between the two types of families, by comparison of reassociation rates at different temperatures, was utilized. The results forVigna defied the predictions of the assay for either homogeneous or hetereogeneous model. Evaluation of the kinetic data in light of the great diversity of repeated family copy numbers in both genomes enabled an interpretation of the results as consistent with hetereogenous families inPisum and homogeneous families inVigna. These tentative conclusions were supported by the results of a thermal denaturation (melting) assay described in the accompanying paper.Abbreviations used C_ot the product of molar concentration of DNA nucleotides and time of incubation (mol s/L) - EC_ot equivalent - C_ot the value after correction to standard reassociation conditions (120 mM sodium phosphate buffer, 60°C) - (Et)₄NCl tetraethylammonium chloride - T_m the temperature at which half of the nucleotides in solution are unpaired This paper is Carnegie Institution of Washington Department of Plant Biology Publication No. 708 and is based on a portion of a dissertation submitted by R.S.P. in partial fulfillment of the Ph.D. requirements at Stanford University