Identification of enhancer elements in the upstream region of the nuclear photosynthetic gene ST-LS1.

The nuclear gene ST-LS1 from potato encodes a 10-kilodalton protein that is a component of the oxygen-evolving complex of photosystem II. Analysis of the expression of a reporter gene driven by chimeric promoters, consisting of ST-LS1 upstream sequences and a truncated cauliflower mosaic virus 35S promoter, suggests that a strong positive regulatory element is located between position -345 and -261, whereas both the region -261 to +11 and the more upstream region -1600 to -530 are devoid of autonomous strong positive elements detectable by this approach. The ST-LS1 upstream region contains redundant elements conferring light-regulated and organ-specific expression, one of them being located between position -130 and +11. In addition, enhancer-like sequences conferring light-regulated as well as organ-specific expression to heterologous promoters were identified. These sequences are functional not only when located 5'-upstream of the coding region but also when placed 3'-downstream of the polyadenylation signal, thus representing one of the first examples of a plant gene-derived enhancer being able to induce a truncated heterologous promoter from a position 3'-downstream of the transcription unit.