Alterations in the phenotype of plant cells studied by NH(2)-terminal amino acid-sequence analysis of proteins electroblotted from two-dimensional gel-separated total extracts

Phenotypic alterations induced by the cytokinin 6-benzylaminopurine in cell suspensions of Nicotiana plumbaginifolia were studied at the level of the NH(2)-terminal sequence of the constituent proteins. Total protein extracts were separated by classical two-dimensional PAGE, and the proteins were recovered by electroblotting onto support materials allowing direct gas-phase sequence analysis of the immobilized proteins. The systems used consist of an efficient electrotransfer buffer (50 mM Tris borate, pH 8.3) in combination with either glass-fiber sheets to which poly(4-vinyl-N-methylpyridinium iodide) is adsorbed or with membranes of polyvinylidene difluoride. The former is an improved version of our previously reported Polybrene-coated glass-fiber sheets and was found to be at least twice as efficient as the polyvinylidene difluoride blots. Thirteen proteins were selected for analysis. They were either induced, repressed, or independent of cytokinin. Ten proteins yielded a sequence, ranging from 10 to 38 residues. Three of the studied Nicotiana proteins show a degree of homology higher than 85% with the amino acid sequences of other eukaryotic proteins-triose-phosphate isomerase, Mn superoxide dismutase, and (1,3)-beta-glucanase. The latter enzyme was repressed by the plant hormone. This study demonstrates that proteins associated with phenotypic variations in cells can now be sequenced by a straightforward procedure involving two-dimensional gel separation of total cellular proteins, recovery by electroblotting, and gas-phase sequence analysis of the immobilized proteins.