To find out the growth conditions for the maximum activity of nitrogenase which catalyzes nitrogen fixation in Rhodobacter sphaeroides, the promoter activities of nifA and nifH were analyzed and the results indicated that expression of both nifA and nifH was increased in response to deprivation of both O2 concentration and nitrogen source. The nifA mutant was constructed by deleting the gene to investigate the effect of NifA, the transcriptional regulator, on the nifH and nifA expression in R. sphaeroides. Analysis of expression of nif genes using the nifA::lacZ and nifH::lacZ fusions in the nifA mutant revealed that NifA acts as a positive activator for nifH and an autoregulator in its own expression. The promoter activities of nifA and nifH in the prrA mutant grown under anaerobic and NH4 +-free conditions were derepressed, comparing with those of the wild-type grown under the same conditions, indicating that the prrA product acts as a positive regulator in expression of nifA and nifH.

Abstract
 1. 서 론
 2. 재료 및 방법
  2.1. 사용 균주, 플라스미드 및 배양 조건
  2.2. DNA 제조 및 conjugation에 의한 형질 전환
  2.3. Transcriptional lacZ fusion plasmid 제작법
  2.4. R. sphaeroidses의 nifA mutant 제작
  2.5. R. sphaeroides nifA mutant 상보성 실험
  2.6. β-galactosidase assay와 단백질 결정
 3. 결과 및 고찰
  3.1. nifA와 nifH 유전자의 최적 발현 조건
  3.2. R. sphaeroides nifA mutant 확인을 위한 nested PCR
  3.3. R. sphaeroides nifA mutant에서의 nifA 및 nifH의 lacZ fusion 활성과 상보성 실험
  3.4. R. sphaeroides prrA mutant에서 nifA::lacZ fusion과 nifH::lacZ fusion의 활성 비교
 4. 결 론
 참 고 문 헌

• 손명화(부산대학교 미생물학과) | Myung-Hwa Son (Department of Microbiology, Pusan National University)
• 김민주(부산대학교 미생물학과) | Min-Ju Kim (Department of Microbiology, Pusan National University)
• 이상준(부산대학교 미생물학과) | Sang-Joon Lee (Department of Microbiology, Pusan National University) Corresponding author