| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2004: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
Complete genome sequence of over 200 microorganisms has been done and paralogous pairs of ribosomal protein genes are found in many bacterial genomes. It has been reported that genes encoding ribosomal protein L31, L33, L36 and S14 are duplicated in several bacterial genomes, and each of them can be classified into two types: one type contains a zinc-binding motif, whereas another doses not. We have shown that two types of L31 protein can be detected in ribosomes prepared from cells at different growth phases in zinc-limiting minimal medium. The RpmE is stable when it contains a zinc ion bound to its CysXXCys motif, and the expression of ytiA, coding for the zinc-lacking form of L31 protein, is, repressed by Zur. We have also shown that when purified YtiA is added to an RpmE-containing ribosome solution in vitro, YtiA-containing ribosomes are detected, thus suggesting that newly synthesized YtiA can liberate RpmE from ribosomes. From these results, we proposed that the change between the two types of L31 proein in the ribosome is triggered by changes in the concentration of zinc in the environment.
We further analyzed another paralogous pair of ribosomal protein genes, rpsN and yhzA, and proposed that the switch between their products has a different significance. rpsN is indispensable for growth and depletion of RpsN results in defective 30S subunits. YhzA can functionally replace RpsN to allow continued ribosome assembly under zinc-limiting conditions. Unlike YtiA, YhzA appeared in the ribosome at a slower rate consistent with incorporation into newly synthesized, rather than pre-existing ribosomes. These results suggested that YhzA is involved in a fale-safe system for the denovo synthesis of ribosomes under zinc-limiting conditions.
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