Abstract: Synechocystis sp.PCC6803 is able to grow on glucose in complete darkness with a daily stimulation of short and weak light, which is called light activated heterotrophic growth (LAHG).By random insertion of a kanamycin-resistance cassette into Hae Ⅲor Alu Ⅰsites of the genome, a mutant library of Synechocystis sp.PCC6803 was constructed.From this library, 3 mu-tants incapable of LAHGbut similar to wild type in autotrophic, mixotrophic and phototrophic growth were selected.Inverse PCR and sequence determination showed that all the insertion were at a Hae Ⅲ (GGCC,6662669Nt.-site of s110886.s110886 without its N2terminal trans-membrane encoding sequence was generated by PCR, cloned into pET-1b and expressed in E.coli BL-1 (DE3).The expressed product, found in the soluble fraction, was purified with the assistance of its C-terminal His.Tag and used to prepare the rabbit antiserum against S110886.Western Blot was employed to investigate the presence of S110886 in membrane or soluble protein fraction of the cyanobacterium, and it was found to be a membrane protein.Using total membrane from cells with different periods of light exposure, the expression of s110886 was examined and found to be non2responsive to il-lumination.We conclude that s110886 is essential to LAHGand not induced by light.