摘要:

Two transcriptional units coding for ribosomal proteins and protein synthesis elongation factors inMethanococcus vannieliihave been cloned and analysed in detail. They correspond to the "streptomycin operon" and "spectinomycin operon" of theEscherichia colichromosome. The following general conclusions can be drawn from comparison of the nucleotide and the derived amino acid sequences of ribosomal proteins fromMethanococcuswith those from eubacteria and eukaryotes. (i) Ribosomal protein and elongation factor genes inMethanococcusare clustered in transcriptional units corresponding closely toE.coliribosomal protein operons with respect to both gene composition and organization. (ii) These transcriptional units contain, in addition, a few open reading frames whose putative gene products share sequence similarity with eukaryotic 80S but not with eubacterial, ribosomal proteins. They may correspond to "additional" ribosomal proteins of theMethanococcusribosome, there being no functional homologues in the eubacterial ribosome. (iii) Methanococcus ribosomal proteins and elongation factors almost exclusively exhibit a higher sequence similarity to eukaryotic 80S ribosomal proteins than to those of eubacteria. (iv) ManyMethanococcusribosomal proteins have a size intermediate between those of their eukaryotic and eubacterial homologues. These results are discussed in terms of a hypothesis which implies that the recent eubacterial ribosome developed by a "minimization" process from a more complex organelle and that the archaebacterial ribosome has maintained features of this ancestor.Key words: archaebacteria,Methanococcus, transcription factors, clonal analysis.

ISSN:0008-4166    

DOI:10.1139/m89-031

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The properties of the halobacterial isolateHalobacteriumsp. GRB are discussed, especially in relation to its use as a laboratory strain. Experimental results on this species are described, including the isolation of point mutants in the bacterioopsin gene leading to single amino acid replacements in bacteriorhodopsin, the application of a selection procedure for the isolation of different types of mutants, the genetic stability ofHalobacteriumsp. GRB and the possibility of isolating a set of isogenic mutants, the conditions for transformation experiments with this species, and specific features ofHalobacteriumsp. GRB, such as halocin production and the absence of a restriction system, as well as DNA adenosine methylation.Key words: halobacteria,Halobacteriumsp. GRB,in vivomutagenesis, 5-bromo-2′-deoxyuridine selection, bacteriorhodopsin.

ISSN:0008-4166    

DOI:10.1139/m89-032

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The structure of the exon–intron boundary was compared for an intron within 23S ribosomal RNA ofDesulfurococcus mobilisand a newly discovered intron in tRNAMetfrom the same organism. The occurrence of a putative common structural feature suggests that intron excision occurs by the same mechanism. The possible recognition of this structural feature by the cleavage enzyme was investigated for the ribosomal RNA intron using RNA substrates exhibiting various exon and intron deletions. The results support the involvement of the structural features in the cleavage process. The evolutionary implications of these results are considered.Key words: archaebacteria, tRNA, ribosomal RNA, introns, intron evolution.

ISSN:0008-4166    

DOI:10.1139/m89-033

出版商:NRC Research Press    

年代:1989

数据来源: NRC

ISSN:0008-4166    

DOI:10.1139/m89-034

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

We have isolated DNA polymerases and topoisomerases from two thermoacidophilic archaebacteria:Sulfolobus acidocaldariusandThermoplasma acidophilum. The DNA polymerases are composed of a single polypeptide with molecular masses of 100 and 85 kDa, respectively. Antibodies againstSulfolobusDNA polymerase did not cross react withThermoplasmaDNA polymerase. Whereas the major DNA topoisomerase activity inS.acidocaldariusis an ATP-dependent type I DNA topoisomerase with a reverse gyrase activity, the major DNA topoisomerase activity inT.acidophilumis a ATP-independent relaxing activity. Both enzymes resemble more the eubacterial than the eukaryotic type I DNA topoisomerase. We have found that small plasmids from halobacteria are negatively supercoiled and that DNA topoisomerase II inhibitors modify their topology. This suggests the existence of an archaebacterial type II DNA topoisomerase related to its eubacterial and eukaryotic counterparts. As in eubacteria, novobiocin induces positive supercoiling of halobacterial plasmids, indicating the absence of a eukaryotic-like type I DNA topoisomerase that relaxes positive superturns.Key words: archaebacteria, DNA topoisomerases, DNA polymerases, DNA topology, gyrase.

ISSN:0008-4166    

DOI:10.1139/m89-035

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The genes corresponding to the L11, L1, L10, and L12 equivalent ribosomal proteins (L11e, L1e, L10e, and L12e) ofEscherichia colihave been cloned and sequenced from two widely divergent species of archaebacteria,Halobacterium cutirubrumandSulfolobus solfataricus, and the L10 and four different L12 genes have been cloned and sequenced from the eucaryoteSaccharomyces cerevisiae. Alignments between the deduced amino acid sequences of these proteins and to other available homologous proteins of eubacteria and eucaryotes have been made. The data suggest that the archaebacteria are a distinct coherent phylogenetic group. Alignment of the proline-rich L11e proteins reveals that the N-terminal region, believed to be responsible for interaction with release factor 1, is the most highly conserved region and that there is specific conservation of most of the proline residues, which may be important in maintaining the highly elongated structure of the molecule. Although L11 is the most highly methylated protein in theE.coliribosome, the sites of methylation are not conserved in the archaebacterial L11e proteins. The L1e proteins of eubacteria and archaebacteria show two regions of very high similarity near the center and the carboxy termini of the proteins. The L10e proteins of all kingdoms are colinear and contain approximately three fourths of an L12e protein fused to their carboxy terminus, although much of this fusion has been lost in the truncated eubacterial protein. The archaebacterial and eucaryotic L12e proteins are colinear, whereas the eubacterial protein has suffered a rearrangement through what appear to be gene fusion events. Within the L12e derived region of the L10e proteins there exists a repeated module of 26 amino acids, present in two copies in eucaryotes, three in archaebacteria, and one in eubacteria. This modular sequence is apparently also present in the L12e proteins of all kingdoms and may play a role in L12e dimerization, L10e–L12e complex formation, and the function of the L10e–L12e complex in translation.Key words: translation, ribosome.

ISSN:0008-4166    

DOI:10.1139/m89-036

出版商:NRC Research Press    

年代:1989

数据来源: NRC