TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL CONTROL OF SUCROSE GENES IN SALT-TREATED CELLS OF SYNECHOCOCCUS SP. PCC 7002.

CUMINO ANDREA; PEREZ CENCI MACARENA; CALÓ GONZALO; SALERNO GRACIELA L

Mar del Plata

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular. SAIB; 2007

Accumulation of compatible solutes that do not interfere with cell metabolism is auniversal process during cellular acclimation to environments with low water potentials.Synechococcus sp. PCC 7002 strain is moderately halotolerant cyanobacterium that synthesizesglucosylglycerol during salt stress as primary osmolite and sucrose like secondary osmolite.But, it was demonstrated that sucrose metabolism belongs to the basal metabolic repertoire inmarine cyanobacteria, in contrast to glucosylglycerol biosynthesis enzymes whose expression isonly detected during a salt stress. On the other hand as similarly occurs in other prokaryota, inSynechococcus sp. pcc 7002 the sucrose accumulation was enhanced during the stationaryphase. Recently, it was elucidated that sucrose synthesis in this strains occurs through thesequential action of sucrose-phosphate synthase (SPS) and sucrose-phosphate phosphatase(SPP) activities. This marine cyanobacterium presents an only gene that encodes for SPS, inagreement with the proposed pattern of the evolution of the metabolism of sucrose and with theevolutionary radiation of the cianobacteria. spsA gene is superimposed 8 nucleotides with thesppA gene, being able to constitute an transcripcional unit with two overlapped cistrons.When we investigated the effect of NaCl and stationary phase on the regulation ofsucrose genes in Synechococcus strains, northern blots experiments revealed independenttranscripts for both genes. We found that the synthesis of the spsA and sppA transcripts wereprevented and the 100% of two mRNA remained 3 h after the introduction of rifampicin. Wethen used RT-PCR using intergenic primers to determine the possible presence of a primarytranscript containing both genes. Only in the presence of chloramphenicol was detected thespsA/sppA transcriptional unit, suggested that protein synthesis is responsible of the primarytranscrip degradation and that they are cotranscribed from a single upstream promoter. Putativepromoters were identified for these cistrons after primer extension analysis. These resultsindicate that in this cyanobacterium, one evolutionary solution for coordinate the sucrose geneexpression.