- ASR1 is a plant-specific, highly charged, low molecular weight polypeptide. Purified ASR1 was shown to posses sequence specific Zn 2+ + + -dependent DNA binding activity (Kalifa et al . Biochemical Journal 381, 373-378, 2004). Steady-state levels of tomato Asr1 mRNA and protein are transiently increased following exposure of plants to poly- ethylene glycol, NaCl or abscisic acid. The biological role of ASR1 could not be deduced from sequence analyses or sequence homologies. Tobacco plants over-expressing tomato ASR1 have a decreased rate of water loss and improved salt tolerance. Upon exposure to salt, ASR1- over-expressing plants accumulate less Na + + + and proline than wild-type plants, and also results in increased steady- state levels of other gene products under non-stressed plant growth conditions. Therefore, ASR1 is probably involved in the regulation of water- or salt-stress-modulated gene expression.