SHI RELATED SEQUENCE(SRS), which encode proteins with a single zinc finger motif. The genes are members of a small gene family of putative transcription factors in which the SHORT INTERNODES (SHI) gene is found.
The predicted amino acid sequence of SHI has acidic and glutamine-rich stretches and shows sequence similarity over a putative zinc finger region to three presumptive Arabidopsis proteins. This suggests that SHI may act as a negative regulator of GA responses through transcriptional control.
The predicted SHI protein consists of 331 amino acids. A region containing six cysteine residues (amino acids 120 to 147) in a C-X2-C-X7-C-X4-C-X2-C-X7-C arrangement (where X is a variable amino acid) is suggested to make up a zinc finger domain similar to the Zn2Cys6 cluster found in the DNA binding region of the yeast transcriptional activator GAL4 (Kraulis et al. 1992 ). Two regions rich in glutamine residues were found adjacent to the zinc finger domain, as well as a short stretch of acidic residues in the C-terminal third of the SHI protein. These features have been found in transcription factor proteins and have been demonstrated to be important for their function as transcriptional activators (Mitchell and Tjian 1989 ). Furthermore, two putative nuclear localization signals (NLSs) were found in the SHI sequence. These are two basic stretches (amino acids 160 to 165 and 183 to 188) that conform to the consensus of the simian virus 40-like ’typical NLS’ defined as four arginines and lysines within a region of six amino acids (Boulikas 1994 ; LaCasse and Lefebvre 1995 ).
