The Bgl Ⅱ fragment carried in plasmid pMH903,which covers the nodD3 region of Rhizobium meliloti, has been sequenced. By using both S1 nuclease mapping and primer extension, two transcription start sites were demonst...The Bgl Ⅱ fragment carried in plasmid pMH903,which covers the nodD3 region of Rhizobium meliloti, has been sequenced. By using both S1 nuclease mapping and primer extension, two transcription start sites were demonstrated in the sequence. After the first transcription start site, there were two open reading frames (ORF) followed by the nodD3 coding sequence which was also preceded by the second promoter.The nodD3 gene under the first promoter mediated high,constitutive expression of nodC-lacZ fusion,and the gene under the second promoter required the product of nodD1 and alfalfa (Medicago sativa) seed exudate for the activation of fusion.Nodulation experiments showed that the nodD3 gene under either promoter was functional in eliciting nodules on alfalfa.The deletion of part of the two ORFs after the first promoter or deletion of the second promoter did not block the constitutive expression of nodC-lacZ fusion, whereas the deletion of the first promoter region or a polar insertion mutation between the two pr moters did cause nodD3 to activate nodC only in the presence of the inducer.It indicates that nodD3 can be transcribed from the first promoter as well as from a separate second promoter.展开更多
LegHb mRNAs isolated from 2 to 10-week old alfalfa nodules are actively translated in vitro to give a full component of legHb products suggesting that legHb genes, once expressed, are not regulated at the transcriptio...LegHb mRNAs isolated from 2 to 10-week old alfalfa nodules are actively translated in vitro to give a full component of legHb products suggesting that legHb genes, once expressed, are not regulated at the transcription level during the lifetime of a nodule. In vitro translation studies with legHb mRNAs from 10-week old nodules indicate that translation of mRNAs is partially inhibited by addition of alfalfa legHb components themselves and is not promoted by addition of myoglobin and hemoglobin as compared with those of alfalfa legHb mRNAs isolated from 4-week old nodules. This intimates that the regulation of alfalfa legHb synthesis in old nodules at the translation level is weakened.展开更多
RNA polymerase Ⅱ from yeast cannot transcribe cDNA of potato spindle tuber viroid (PSTV), in spite of its ability to transcribe in vitro PSTV faithfully. RNA polymerase from E. coli is capable of transcribing both PS...RNA polymerase Ⅱ from yeast cannot transcribe cDNA of potato spindle tuber viroid (PSTV), in spite of its ability to transcribe in vitro PSTV faithfully. RNA polymerase from E. coli is capable of transcribing both PSTV and its cDNA. PAGE analysis of transcripts, Southern molecular hybridization and experiments to exclude the possibility of terminal labeling of template indicate that the transcription of PSTV cDNA by E. coli RNA polymerase is a faithful one. This paper first presents the idea that PSTV cDNA constitutes a transcriptional unit containing a promoter-like region capable of directing specific initiation of transcription. It is proved that the promoter is located on the 132 bp small fragment obtained after cleavage of PSTV cDNAwith AvaII, probably lying around the BamHl site in the 5’terminus.展开更多
基金Project supported by the National Natural Science Foundation of China.
文摘The Bgl Ⅱ fragment carried in plasmid pMH903,which covers the nodD3 region of Rhizobium meliloti, has been sequenced. By using both S1 nuclease mapping and primer extension, two transcription start sites were demonstrated in the sequence. After the first transcription start site, there were two open reading frames (ORF) followed by the nodD3 coding sequence which was also preceded by the second promoter.The nodD3 gene under the first promoter mediated high,constitutive expression of nodC-lacZ fusion,and the gene under the second promoter required the product of nodD1 and alfalfa (Medicago sativa) seed exudate for the activation of fusion.Nodulation experiments showed that the nodD3 gene under either promoter was functional in eliciting nodules on alfalfa.The deletion of part of the two ORFs after the first promoter or deletion of the second promoter did not block the constitutive expression of nodC-lacZ fusion, whereas the deletion of the first promoter region or a polar insertion mutation between the two pr moters did cause nodD3 to activate nodC only in the presence of the inducer.It indicates that nodD3 can be transcribed from the first promoter as well as from a separate second promoter.
文摘LegHb mRNAs isolated from 2 to 10-week old alfalfa nodules are actively translated in vitro to give a full component of legHb products suggesting that legHb genes, once expressed, are not regulated at the transcription level during the lifetime of a nodule. In vitro translation studies with legHb mRNAs from 10-week old nodules indicate that translation of mRNAs is partially inhibited by addition of alfalfa legHb components themselves and is not promoted by addition of myoglobin and hemoglobin as compared with those of alfalfa legHb mRNAs isolated from 4-week old nodules. This intimates that the regulation of alfalfa legHb synthesis in old nodules at the translation level is weakened.
基金Project supported by the National Natural Science Foundation of China
文摘RNA polymerase Ⅱ from yeast cannot transcribe cDNA of potato spindle tuber viroid (PSTV), in spite of its ability to transcribe in vitro PSTV faithfully. RNA polymerase from E. coli is capable of transcribing both PSTV and its cDNA. PAGE analysis of transcripts, Southern molecular hybridization and experiments to exclude the possibility of terminal labeling of template indicate that the transcription of PSTV cDNA by E. coli RNA polymerase is a faithful one. This paper first presents the idea that PSTV cDNA constitutes a transcriptional unit containing a promoter-like region capable of directing specific initiation of transcription. It is proved that the promoter is located on the 132 bp small fragment obtained after cleavage of PSTV cDNAwith AvaII, probably lying around the BamHl site in the 5’terminus.
