The region of the ultraviolet betxeen about 220 mp and the onset of opacity due to the water absorption band (ca. 185 mp) has recently become accessible to commercially available photoelectric spectrophotometers (see, for example, Kaye') as a result of the development of synthetic quartz optics of high transparency in this range. This region of the spectrum is of especial interest, containing as it does the absorption bands of isolated double bonds, amides, and related compounds, and also the higher energy T-T* transitions of aromatic molecules. A number of results of both analytical and theoretical interest in biochemistry have already been obtained from spectrophotometric studies in the far ultraviolet region, the more obvious examples being with steroids223 and polypeptides and p r~t e i n s .~.~ An examination of the absorption spectra of the nucleic acids and their various components in the far ultraviolet can be expected to be of general interest. RIore specifically, such results should be useful in the theoretical iiwestigations of the origin of the hypochromic effects (see, for example, TinocoG and Rhodes7) and in practical applications such as the estimation of the amount of secondary structure or the degree of denaturation,s the analysis of nucleotide mixturesJg and the identification of the doniinaiit composition of regions of nucleic acid molecules displaying selective denaturationlo which have thus far been limited to the use of measurements in the 260 mp region. This paper consists of a systematic presentation of such spectra and brief comment upon them. EXPERIMENTAL MaterialsPurine and pyrimidine bases, nucleosides, nucleotides, and sugars were obtained from the California Biochemical Corporation; purine, pyrimidine, and ~-ribosed-phosphate from JIann Research Laboratories. According to the manufacturers the samples were chromatographically pure. We are indebted to R. Thach for samples of polynucleotides, to Dr. H. Boedtker for samples of soluble ribonucleic acid (sRSA), and to Drs. J. Marmur and R. Rownd for samples of deoxyribonucleic acid (DKA).

No abstract

Mycobacterium tuberculosis is a prototrophic, metabolically flexible bacterium that has achieved a spread in the human population that is unmatched by any other bacterial pathogen. The success of M. tuberculosis as a pathogen can be attributed to its extraordinary stealth and capacity to adapt to environmental changes throughout the course of infection. These changes include: nutrient deprivation, hypoxia, various exogenous stress conditions and, in the case of the pathogenic species, the intraphagosomal environment. Knowledge of the physiology of M. tuberculosis during this process has been limited by the slow growth of the bacterium in the laboratory and other technical problems such as cell aggregation. Advances in genomics and molecular methods to analyse the M. tuberculosis genome have revealed that adaptive changes are mediated by complex regulatory networks and signals, resulting in temporal gene expression coupled to metabolic and energetic changes. An important goal for bacterial physiologists will be to elucidate the physiology of M. tuberculosis during the transition between the diverse conditions encountered by M. tuberculosis. This review covers the growth of the mycobacterial cell and how environmental stimuli are sensed by this bacterium. Adaptation to different environments is described from the viewpoint of nutrient acquisition, energy generation and regulation. To gain quantitative understanding of mycobacterial physiology will require a systems biology approach and recent efforts in this area are discussed. “It is now 100 years since the first mycobacterium was isolated by Hansen (1874). Somewhat ironically, this was the leprosy bacillus, Mycobacterium leprae, which even today is still resisting all attempts to cultivate it in the laboratory. The tubercle bacillus, M. tuberculosis was not discovered until eight years later (Koch, 1882) and this has remained an object of intensive investigation ever since. The widespread interest in the mycobacteria of course stems from the diseases they cause and, lest it be imagined that tuberculosis is a disease which has now been largely conquered and that leprosy is of relatively rare occurrence, current estimates for the number of case of tuberculosis and leprosy in the world today are 20,000,000 and 11,000,000, respectively (Bechelli and Dominguez, 1972). The annual estimated mortality rate is equally dramatic, namely 3,000,000 (World Health Organization, 1974). Also causing unease is the continuing isolation from tubercular patients of strains already resistant to one or more chemotherapeutic agent”. C. Ratledge (1976).

Mycobacterium smegmatis has two rRNA (rm) operons designated rrnA, and rrnB,. Appropriate restriction fragments of genomic DNA containing sequences immediately upstream from the 165 rRNA genes were cloned. We now report the nucleotide sequence of 552 bp upstream from the 5'-end of the Box A, antitermination element of the leader region of the rrnAf operon. The 5'-end of this segment of DNA was found to comprise 113 codons of an ORF encoding a protein which is significantly similar to UDP-N-acetylglucosamine 1-carboxyvinyl-transferase (EC 2.5.1.7), which is important to cell wall synthesis. A homologous ORF is located immediately upstream from the single rrn (rrnAJ operons of Mycobacterium tuberculosis and Mycobacterium leprae. Primer-extension analysis of the RNA fraction of M. smegmatis revealed four products which were related to transcription start points; the rrnb?, operon appears to have a single promoter whereas the rrnA, operon has three (PI, P2 and P3). Analysis of M. tuberculosis RNA revealed two products corresponding to transcripts directed by promoters homologous with P I and P3 of the nnA, of M. smegmatis. Thus, the promoter and upstream regions of the mnA, operon of M. smegmatis and the rrnAs operon of M. tuberculosis are homologous. The presence of P2 in M. smegmatis and its absence from M. tuberculosis is attributable to insertionddeletions of 97 bp.

No abstract