[Show abstract][Hide abstract] ABSTRACT: The yeast two-hybrid system was used to investigate dimerization between proteins ofPhz2 andPhz4 clones of the homeodomain-leucine zipper family which were obtained by screening aPimpinella brachycarpa shoot-tip cDNA library. Assays showed that Phz4 formed a homo rather than a heterodimer with Phz2. In addition, we isolated
cDNA clones,Phyb1, Phyb2, andPhyb3, that encode proteins interacting with Phz4. Although Phyb1 is not a HD-Zip protein, the activity of interaction between
Phyb1 and Phz4 was, surprisingly, stronger than that of the homodimerization of Phz4. The analysis of interacting parts indicated
that from 1 bp to 466 bp of Phyb1, there was no interaction with Phz4, but from 467 bp to 593 bp, interactions were found
with the N-terminal and C-terminal regions, except for HD-Zip of Phz4. This region ofPhyb1 contained a nuclear localization signal. DNA-binding analysis showed that the Phz4 HD-Zip domain recognized the [T(C/G)ATTG]
core sequence and the region containing the [TCATTG] motif, which is, in itself, a promoter in vitro.
[Show abstract][Hide abstract] ABSTRACT: Using a tobacco cDNA clone as a probe, a genomic clone named TUQG-4, coding for a tobacco polyubiquitin protein with the five
head-to-tail repeats of ubiquitin monomer was isolated. The five ubiquitin units were completely conserved except for the
extra phenylalanine at the carboxy terminus of the last ubiquitin monomer. The putative open reading frame identified from
the nucleotide sequence showed two possible intron sequences in the coding region for the first ubiquitin monomer. When the
amino acid sequence deduced from the nucleotide sequence of TUQG-4 was compared to the amino acid sequences coded by other
polyubiquitin genes of tobacco, there were three or four amino acid differences in the sequence. When the nucleotide sequences
coding for the ubiquitin monomers were compared for various species origins, the degree of identity was at the highest between
the ubiquitin monomers in one polyubiquitin and did not reflect the distance of the phylogenetic relationship.