Transposable Elements In Peas

Klug and Cummings state that the wrinkled peas that Mendael studied to evaluate discreet segregation ratios were caused by a transposable element. The wrinkled phenotype is due to the fact that these seeds lose more water than smooth seeds because of the absence of a starch-branching enzyme (SBEI). "The structural gene for SBEI has now been cloned and characterized in both wild-type and mutant genotypes. In the rr (wrinkled) genotype, the SBEI protein is nonfunctional, presumably because the SBEI gene is interrupted by a 0.8-kb insertion, resulting in the production of an abnormal RNA transcript. The inserted DNA has 12- bp inverted repeates at each end that are highly homologous to the terminal sequences in the transposable element Ac from maize, and other Ac-like elements form snapdragons and parsley. Terminal repeated sequences and the genetic information encoding a transposase enzyme appear to be universal components of transposons in all organisms studied."