Structure and expression of ubiquitin genes in higher plants.

cDNA clones encoding ubiquitin were isolated from a barley leaf cDNA library using a mammalian ubiquitin cDNA clone as probe. The nucleotide sequence of one of the clones codes for 2.2 perfect repeats of the 76-amino-acid-long ubiquitin protein with an extra lysine residue at the C-terminus. The barley ubiquitin amino acid sequence differs from the animal sequence at three positions and from the yeast sequence at two positions. The ubiquitin poly(precursor) are coded by a multigene family with 8-10 genes that produce four or five different size messengers between 700 and 2000 nucleotides in length. The large poly(A)-rich RNAs are constitutively expressed in vegetative tissues whereas the 700-nucleotide messenger(s) were only detected in tissues containing dividing cells.