Acetate Kinase Isozymes Confer Robustness in Acetate Metabolism

Acetate kinase (ACK) (EC no: 2.7.2.1) interconverts acetyl-phosphate and acetate to either catabolize or synthesize acetyl-CoA dependent on the metabolic requirement. Among all ACK entries available in UniProt, we found that around 45% are multiple ACKs in some organisms including more than 300 species but surprisingly, little work has been done to clarify whether this has any significance. In an attempt to gain further insight we have studied the two ACKs (AckA1, AckA2) encoded by two neighboring genes conserved in Lactococcus lactis (L. lactis) by analyzing protein sequences, characterizing transcription structure, determining enzyme characteristics and effect on growth physiology. The results show that the two ACKs are most likely individually transcribed. AckA1 has a much higher turnover number and AckA2 has a much higher affinity for acetate in vitro. Consistently, growth experiments of mutant strains reveal that AckA1 has a higher capacity for acetate production which allows faster growth in an environment with high acetate concentration. Meanwhile, AckA2 is important for fast acetate-dependent growth at low concentration of acetate. The results demonstrate that the two ACKs have complementary physiological roles in L. lactis to maintain a robust acetate metabolism for fast growth at different extracellular acetate concentrations. The existence of ACK isozymes may reflect a common evolutionary strategy in bacteria in an environment with varying concentrations of acetate

Identification of a new gene product encoded by mRNA D of Infectious Bronchitis Virus.

The coronavirus Infectious Bronchitis Virus (IBV), a pathogen of chickens, has a genome structure typical of a coronavirus. The virus particle contains a single-stranded RNA molecule of approximately 27kb with positive polarity, and in infected cells six species of virus-specific mRNA are produced, designated RNA A to RNA F in order of increasing size (RNA F corresponding to the size of the genomic RNA). These RNAs form a nested set, in which the sequences in each of the subgenomic RNAs are also represented in all the larger RNAs; these RNA species each have a short ‘leader’ sequence corresponding to the 5′ end of the genomic RNA followed by progressively larger amounts of information derived from its 3′ -end. For each mRNA, the region of sequence which is not contained in the next smallest RNA is assumed to be used for translation of viral proteins. Polypeptide products have been assigned for RNAs A, C and E (nucleoprotein, membrane protein and the spike protein precursor respectively), but the coding function of the other RNAs has not so far been established, although it has generally been assumed that RNA F codes for the viral RNA-dependent-RNA-polymerase.Peer reviewe