A putative gene encoding the RNA chaperone Hfq can be predicted in two of the four marine cyanobacteria investigated here. (a) The dapF-leuS intergenic region in Synechococcus WH 8102 (WH8) and Prochlorococcus MIT 9313 (MIT) is, at 298 and 297 nucleotides, respectively, relatively long and contains a short reading frame for a putative hfq gene. In Prochlorococcus SS120 (SS1) and MED4 (MED), this region is only 123 and 108 nucleotides, respectively. (b) Sequence comparison of putative Hfq proteins from the three cyanobacteria Synechocystis PCC 6803 (ssr3341 gene), Synechococcus WH 8102 (WH8) and Prochlorococcus MIT 9313 (MIT). Hydrophobic residues within the Sm1 and Sm2 motifs  are indicated by an H.