• Korean Journal of Microbiology
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• v.48 no.2
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• pp.79-86
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• 2012

ErmSF is one of the Erm family proteins which catalyze S-adenosyl-$_L$-methionine dependent modification of a specific adenine residue (A2058, E. coli numbering) in bacterial 23S rRNA, thereby conferring resistance to clinically important macrolide, lincosamide and streptogramin B ($MLS_B$) antibiotics. $^{222}FXPXPXVXS^{230}$ (ErmSF numbering) sequence appears to be a consensus sequence among the Erm family. This sequence was supposed to be involved in direct interaction with the target adenine from the structural studies of Erm protein ErmC'. But in DNA methyltarnsferase M. Taq I, this interaction have been identified biochemically and from the complex structure with substrate. Arginine 223 and 227 in this sequence are not conserved among Erm proteins, but because of the basic nature of residues, it was expected to interact with RNA substrates. Two amino acid residues were replaced with Ala by site-directed mutagenesis. Two mutant proteins still maintained its activity in vivo and resistant to the antibiotic erythromycin. Compared to the wild-type ErmSF, R223A and R227A proteins retained about 50% and 88% of activity in vitro, respectively. Even though those arginine residues are not essential in the catalytic step, with their positive charge they may play an important role for RNA binding.

• Journal of Life Science
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• v.22 no.4
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• pp.559-564
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• 2012

In order to investigate the effect of phytochromes on the regulation of ethylene biosynthesis, we measured the ethylene production and the activities of enzymes involved in ethylene biosynthesis using phytochrome mutants such as $phyA$, $phyB$, and $phyAB$ of Arabidopsis. The ethylene production was decreased in mutants grown in white light. In particular, double mutants showed a 37% decrease compared to the wild type in ethylene production. When Arabidopsis roots were grown in the dark, mutants did not show a decrease in ethylene production; however, production was significantly decreased in the double mutant grown in red light. Only $phyB$ did not show the decrease in the ethylene production in far-red light. Unlike the ACO activities, the ACS activities of mutants showed the same pattern as the ethylene production under several light conditions. The results of ACS activities confirmed the expression of the ACS gene by RT-PCR analysis. The decrease of ethylene production in mutants was due to the lower activity of ACC synthase, which converts the S-adenosyl-L-methionine (AdoMet) to 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene. These results suggested that both phytochrome A and B play an important role in the regulation of ethylene biosynthesis in Arabidopsis roots in the conversion step of AdoMet to ACC, which is regulated by ACS.

• Journal of Life Science
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• v.22 no.1
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• pp.87-91
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• 2012

Phorbol 12-myristate 13-acetate (PMA), a known tumor-promoting phorbol ester, activates the signal transduction enzyme protein kinase C (PKC) in animal cells. We investigated the effect of PMA on the regulation of gravitropism via ethylene production in primary roots of maize. PMA stimulated root growth and the gravitropic response in a concentration-dependent manner at $10^{-6}$ M and $10^{-4}$ M over 8 hrs. These effects were prevented by treatment with staurosporine (STA), a potent inhibitor of PKC. These results support the possibility that the gravitropic response might be regulated through protein kinases that are involved in the signal transduction system. Ethylene is known to play a role in the regulation of root growth and gravitropism. Ethylene production was increased by about 26% and 37% of the control rate in response to $10^{-6}$ M and $10^{-4}$ M PMA, respectively. PMA also stimulated the activity of ACC synthase (ACS), which converts the S-adenosyl-L-methionine (AdoMet) to 1-aminocyclopropane-1-carboxylic acid (ACC) in the ethylene production pathway. These effects on ethylene production were also prevented by STA treatment. These results suggest that the root gravitropic response in maize is regulated through protein kinases via ethylene production.