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51.
Evidence for effect of random genetic drift on G+C content after lateral transfer of fucose pathway genes to Escherichia coli K-12 总被引:4,自引:0,他引:4
The cps cluster of Escherichia coli K-12 comprises genes involved in
synthesis of capsular polysaccharide colanic acid. Part of the E. coli K-12
cps region has been cloned and sequenced and compared to its Salmonella
enterica LT2 counterpart. The cps genes from the two organisms are
homologous; in the case of the LT2 genes, with G+C content of 0.61 and
codons characteristic of high G+C species, it seems clear that they have
been acquired relatively recently by lateral transfer from a high G+C
species. The K-12 form of these cps genes is closely related to those of
LT2 so must derive from the same high G+C species, but it appears to have
transferred much earlier such that random genetic drift has brought P3 (the
corrected G+C content of codon base 3) down from 0.77 to 0.64, more than
halfway to the E. coli average of 0.57. We estimate, using an equation
developed by Sueoka, that the lateral transfer to E. coli took place
approximately 45 million years ago. This is the first report we are aware
of demonstrating the expected adjustment of P3 after lateral transfer
between species with different G+C content DNA.
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52.
Subunit structure in the walls of sectioned microtubules was first noted by Ledbetter and Porter (6), who clearly showed that certain microtubules of plant meristematic cells have 13 wall protofilaments when seen in cross section. Earlier, protofilaments of microtubular elements had been described in negatively stained material, although exact counts of their number were difficult to obtain. In microtubular elements of axonemes, some success has been achieved in visualizing protofilaments in conventionally fixed and sectioned material (8, 10); much less success has been achieved in identifying and counting protofilaments of singlet cytoplasmic microtubules. By using glutaraldehyde-tannic acid fixation, as described by Misuhira and Futaesaku (7), Tilney et al. (12) studied microtubules from a number of sources and found that all have 13 protofilaments comprising their walls. These authors note that "...the number of subunits and their arrangement as protofilaments appear universal...". Preliminary studies of ventral nerve cord of crayfish fixed in glutaraldehyde-tannic acid indicated that axonal microtubules in this material possess only 12 protofilaments (4). On the basis of this observation, tannic acid preparations of several other neuronal and non-neuronal systems were examined. Protofilaments in microtubules from these several cell types are clearly demonstrated, and counts have been made which show that some kinds of microtubules have more or fewer protofilaments than the usual 13 and that at least one kind of microtubule has an even rather than an odd number. 相似文献
53.
Genes essential for the production of a linear, bacterial (1-->3)-beta-
glucan, curdlan, have been cloned for the first time from Agrobacterium sp.
ATCC31749. The genes occurred in two, nonoverlapping, genomic fragments
that complemented different sets of curdlan( crd )-deficient
transposon-insertion mutations. These were detected as colonies that failed
to stain with aniline blue, a (1-->3)-beta-glucan specific dye. One
fragment carried a biosynthetic gene cluster (locus I) containing the
putative curdlan synthase gene, crdS, and at least two other crd genes. The
second fragment may contain only a single crd gene (locus II).
Determination of the DNA sequence adjacent to several locus I mutations
revealed homology to known sequences only in the cases of crdS mutations.
Complete sequencing of the 1623 bp crdS gene revealed highest similarities
between the predicted CrdS protein (540 amino acids) and glycosyl
transferases with repetitive action patterns. These include bacterial
cellulose synthases (and their homologs), which form
(1-->4)-beta-glucans. No similarity was detected with putative
(1-->3)- beta-glucan synthases from yeasts and filamentous fungi.
Whatever the determinants of the linkage specificity of these beta-glucan
synthases might be, these results raise the possibility that
(1-->3)-beta-glucans and (1-->4)-beta-glucans are formed by related
catalytic polypeptides.
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54.
M Kale R Ramsey-Goldman S Bernatsky MB Urowitz D Gladman PR Fortin M Petri E Yelin S Manzi S Edworthy O Nived S-C Bae D Isenberg A Rahman JG Hanly C Gordon S Jacobsen E Ginzler DJ Wallace GS Alarcón MA Dooley L Gottesman K Steinsson A Zoma J-L Senécal S Barr G Sturfelt L Dreyer L Criswell J Sibley JL Lee AE Clarke 《Arthritis research & therapy》2012,14(Z3):A15
55.
Isozyme electrophoresis was used to assess possible cospeciation of
parasites (cestodes of the Progamotaenia festiva complex) and their hosts
(Australian diprotodont marsupials) and to compare the extent of
interspecific genetic diversity of the parasites and their hosts. On the
basis of morphology, there are three species in the complex, although
electrophoresis revealed 14 distinct genetic types, most of which were host
specific, although there were three cases of apparent host switching. The
evolutionary relationships among the parasites were only partially
concordant with those among the hosts. Moreover, the extent of
electrophoretic diversity among the parasites was much higher than that
among hosts.
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56.
57.
Russell L Legg Jessica R Tolman Cameron T Lovinger Edwin D Lephart Kenneth DR Setchell Merrill J Christensen 《Reproductive biology and endocrinology : RB&E》2008,6(1):57
Background
High dietary intake of selenium or soybean isoflavones reduces prostate cancer risk. These components each affect androgen-regulated gene expression. The objective of this work was to determine the combined effects of selenium and isoflavones on androgen-regulated gene expression in rat prostate. 相似文献58.
Lihong?BuEmail author Kenneth?DR?Setchell Edwin?D?Lephart 《Reproductive biology and endocrinology : RB&E》2005,3(1):58
Background
Isoflavones, the most abundant phytoestrogens in soy foods, are structurally similar to 17beta-estradiol. Few studies have examined the nociception and stress hormone responses after consumption of soy isoflavones. 相似文献59.
Trent?D?LundEmail author Daniel?J?Munson Herman?Adlercreutz Robert?J?Handa Edwin?D?Lephart 《Reproductive biology and endocrinology : RB&E》2004,2(1):5
Background
It is well established that the growth of the prostate gland is a hormone-dependent phenomenon involving both androgenic and estrogenic control. Proliferation of prostate cells is, at least in part, under control of estrogen receptor beta (ER-beta). Phytoestrogens bind ER-beta with high affinity and therefore may have antiproliferative effects in the prostate. 相似文献60.
Lephart ED Call SB Rhees RW Jacobson NA Weber KS Bledsoe J Teuscher C 《Biology of reproduction》2001,64(2):571-578
Steroid hormones, particularly 17beta-estradiol (E2), regulate the development and expression of neural structures and sexual behavior. Recently, we demonstrated that E2-regulated responses are controlled by quantitative trait loci. In this study, we quantified 1) volume of the sexually dimorphic nucleus (SDN) of the preoptic area (POA); 2) medial basal hypothalamic (MBH)-POA aromatase and 5alpha-reductase enzyme activities during prenatal development and in adults; 3) serum LH, testosterone, FSH, E2, prolactin (PRL), and corticosterone levels; 4) reproductive organ (i.e., testis and ventral prostate) weights; and 5) male mating behavior in Noble (NB/Cr) and Wistar-Furth (WF/NCr) rat strains to determine the genetic influence on the measured parameters. Maximal phenotypic divergence in male SDN-POA volumes was seen between NB/Cr versus WF/NCr and BDIX/Cr rats (among nine rat strains initially examined), with the average SDN-POA volume of NB/Cr male rats being significantly greater ( approximately 30%) than that of either WF/NCr or BDIX/Cr males. Subsequent experiments investigated WF/NCr versus NB/Cr male rats in further detail. Significantly higher MBH-POA aromatase activity was seen in adult WF/NCr versus NB/Cr males, while MBH-POA 5alpha-reductase rates were not significantly different (within or between sex) for the two rat strains assayed. Serum LH levels were significantly higher (by greater than sixfold) in WF/NCr versus NB/Cr males, whereas testis organ:body weight and ventral prostate:body weight ratios in WF/NCr versus NB/Cr males were significantly smaller (by approximately 6-fold for testis and approximately 1.5-fold for prostate values). Serum FSH levels were significantly higher (by twofold) in WF/NCr versus NB/Cr males. However, serum testosterone levels were not significantly different, whereas E2 levels were approximately twofold higher (but not significantly different) in WF/NCr versus NB/Cr animals. No significant differences were found in basal (i.e., nonstress) serum PRL or corticosterone levels between the WF/NCr and NB/Cr males. In male copulatory tests, NB/Cr males exhibited significantly more aggressive sexual behavior (e.g., in mounting, intromission, and ejaculation parameters) compared with WF/NCr males. Taken together, these findings indicate that WF/NCr males are, in general, low responders, whereas NB/Cr males are high responders to hormonal signals. The obtained data suggest that the correlative, phenotypic variation in SDN-POA volume (i.e., structure) and reproductive hormone patterns and mating behavior (i.e., function) of WF/NCr versus NB/Cr males is regulated by potentially E2-mediated mechanisms that are genetically controlled. 相似文献