COMPOSITIONAL PROPERTIES OF HOMOLOGOUS CODING SEQUENCES FROM PLANTS

In this work, we investigated (1) the compositional distributions of a ll available nuclear coding sequences (and of their three codon positi ons) of six dicots and four Gramineae; this considerably expanded our knowledge about the differences previously seen between these two grou ps of plants; (2) the compositional correlations of homologous genes f rom dicots and from Gramineae, as well as from both groups; all correl ations were characterized by very good coefficients, with slopes close to unity in the former two cases and very high in the last; (3) the c ompositional transition that accompanied the emergence of Gramineae fr om an ancestral monocot; (4) the compositional correlations between ex ons and introns, which were very good in Gramineae, but only poor to g ood in dicots; and (5) the compositional profiles of homologous genes from angiosperms, which were characterized by a series of peaks (exons ) and valleys (introns) separated by 15-20% GC. The conservative and t ransitional modes of compositional evolution in plant genes and their general implications are discussed.