Heterogeneity of the amino acid sequence of phytochrome from etiolated oat seedlings

Abstract
Phytochrome from etiolated oat seedlings was digested with subtilisin. A 16 kDa fragment was isolated and investigated by microsequencing. Its amino‐terminal sequence SLPGGSMEV/ML revealed a heterogeneity (valine and methionine) at position 9. This proves expression of several phytochrome genes on the protein level. One can conclude from the ratio valine/methionine that the isophytochrome derived from AP5 (containing methionine) is a major gene product besides isophytochromes derived from genes AP4 and AP3 (containing valine).