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The availability of a large number of tRNA sequences has created a need for computer programs to store the data. A program written in FORTRAN language allows one to store tRNA sequences and to retrieve information. The data are stored in such a way that it allows a direct comparison of various tRNA sequences. Moreover, the program draws the 'cloverleaf' structure of any stored tRNA sequence and also provides the characteristics of minor, modified nucleosides and major references. Additions and corrections to the program and stored data can be made easily and an individual does not need computer programming skills to use the program.
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OBJECTIVE: To perform a systematic review of the literature to determine whether singleton pregnancies resulting from IVF-ET/GIFT are at higher risk for preterm birth (<37 weeks). DESIGN: Literature search and systematic review. SETTING: Medical school. INTERVENTION(S): A MEDLINE search (1965-2000) was performed using the terms "premature labor," "infertility," "pregnancy complications," "gonadotropins," "pregnancy outcome," "preterm delivery," and "in vitro fertilization." Criteria for inclusion were English language, original research article, study patients conceived using IVF-ET (with or without intracytoplasmic sperm injection) or GIFT, pregnancy outcome reported compared with a control group (e.g., naturally conceived singletons at their hospital or a national reference), and prematurity clearly defined. Incomplete articles (e.g., abstracts), reports of other studies, and studies that failed to separate multiple from singleton gestations were excluded. MAIN OUTCOME MEASURE(S): Summary of relative risks of preterm birth. RESULT(S): Twenty-seven articles met all inclusion/exclusion criteria and were analyzed by meta-analysis. The random-effects summary relative risk of preterm birth in singleton pregnancies resulting from IVF-ET/GIFT was 1.98 (95% confidence interval, 1.77-2.22). CONCLUSION(S): The risk of preterm birth in singleton pregnancies resulting from IVF-ET/GIFT is twice that of natural conceived pregnancies.
It seems that assisted reproduction technology does not increase the rate of chromosome abnormalities, and up to now, a few cases have been reported. The case we describe here is the first one of monosomy 4q31 in a full-term liveborn after a combined GIFT-IVF procedure. Once more, this case raises the question of whether pregnancies resulting from IVF should be monitored for chromosome abnormalities or not.
OBJECTIVE: To compare the influence of incongruent (asymmetric) follicular development on treatment outcome in IVF-ET and GIFT cycles. DESIGN: A retrospective comparative study. SETTING: Tertiary referral center for infertility. PATIENT(S): Five hundred forty-three consecutive assisted reproduction cycles (428 IVF-ET and 115 GIFT) in 422 infertile patients. INTERVENTION(S): Controlled ovarian hyperstimulation (COH) and IVF-ET or GIFT. MAIN OUTCOME MEASURE(S): The incongruity ratio as a parameter of the asymmetry in follicular development and pregnancy rate (PR). RESULT(S): For GIFT cycles, the PRs were 37.8% and 15.7% in cycles with congruent and incongruent follicular development, respectively. However, for IVF-ET cycles, the PR was not affected by incongruent follicular development: 28.2% and 29.0%, respectively. An inverse relationship was observed between the degree of incongruity and the estimated probability of pregnancy in GIFT cycles but not in IVF-ET cycles. Neither the side of the dominant ovary nor the degree of incongruity were consistent in consecutive cycles. CONCLUSION(S): Incongruent follicular development during COH has a significantly negative influence on the outcome of GIFT cycles but not on the outcome of IVF-ET cycles. The reason for this difference is not clear. We recommend considering IVF-ET instead of GIFT if incongruent follicular development occurs.
The low-temperature phosphorescence and the optically detected magnetic resonance (ODMR) spectra of Escherichia coli tRNA2Glu and its anticodon-anticodon complex with yeast tRNAPhe are reported. The ODMR signals are assigned to the modified base 5-[(methylamino)-methyl]-2-thiouracil (mnm5S2U) located at the "wobble" position of the anticodon. The zero-field splittings (zfs) are larger than those found for 1-methyl-2-thiouracil previously studied in a 1-methyluracil host system by ODMR. They are comparable, however, to those found for neat, polycrystalline 1-methyl-2-thiouracil and for the latter dissolved in ethyl acetate solvent. In the polycrystalline sample, five traps with widely varying zfs are assigned. A very large (15-25%) reduction in the D parameter of mnm5S2U is found to occur on formation of the anticodon-anticodon complex with yeast tRNAPhe. Additional ODMR signals found in the complex are assigned to the wybutine base of yeast tRNAPhe. The extreme sensitivity of the zfs parameters of S2U to environmental perturbations is ascribed to the variable involvement of the heavy atom containing chromophore, C = S, in the triplet-state wave function, which is largely localized on the C = C - C = O portion of the molecule.
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The covalent cross-linking of unmodified Escherichia coli N-acetylvalyl-tRNA to the 16S RNA of Escherichia coli ribosomes upon near-UV irradiation previously reported by us [Schwartz, I., & Ofengand, J. (1978) Biochemistry 17, 2524--2530] has been studied further. Up to 70% of the unmodified tRNA, nonenzymatically bound to tight-couple ribosomes at 7 mM Mg2+, could be cross-linked by 310--335-nm light. Covalent attachment was solely to the 16S RNA. It was dependent upon both irradiation and the presence of mRNA but was unaffected by the presence or absence of 4-thiouridine in the tRNA. The kinetics of cross-linking showed single-hit behavior. Twofold more cross-linking was obtained w-th tight-couple ribosomes than with salt-washed particles. Puromycin treatment after irradiation released the bound N-acetyl[3H]valine, demonstrating that the tRNA was covalently bound at the P site and that irradiation and covalent linking did not affect the peptidyl transferase reaction. Cross-linking was unaffected by the presence of O2, argon, ascorbate (1 mM), or mercaptoethanol (10 mM). Prephotolysis of a mixture of tRNA and ribosomes in the absence of puly(U2,G) did not block subsequent cross-linking in its presence nor did it generate any long-lived chemically reactive species. There was a strong tRNA specificity. E. coli tRNA1Val and tRNA1Ser and Bacillus subtilis tRNAVal and tRNAThr could be cross-linked, but E. coli tRNA2Val, 5-fluorouracil-substituted tRNA1Val, tRNAPhe, or tRNAFMet could not. By sequence comparison of the reactive and nonreactive tRNAs, the site of attachment in the tRNA was deduced to be the 5'-anticodon base, cmo5U, or ,o5U in all of the reactive tRNAs. The attachment site in 16S RNA is described in the accompanying paper [Zimmerman, R. A., Gates, S. M., Schwartz, I., & Ofengand, J. (1979) Biochemistry (following paper in this issue)]. The link between tRNA and 16S RNA is either direct or involves mRNA bases at most two nucleotides apart since use of the trinucleotide GpUpU in place of poly(U2,G) to direct the binding and cross-linking of N-acetylvalyl-tRNA to the P site did not affect either the rate or yield of cross-linking. Both B. subtilis tRNAVal (mo5U) and E. coli tRNA1Val (cmo5U) gave the same rate and yield of cross-linking when directed by the trinucleotide GpUpU. Therefore, the presence of the charged carboxyl group in the cmo5U-containing tRNA apparently does not markedly perturb the orientation of this base with respect to its reaction partner in the 16S RNA. The cross-linking of AcVal-tRNA only takes place from the P site. At 75 mM KCl and 75 mM NH4Cl, less than 0.4% cross-linking was found at the A site, while 55.5% was obtained at the P site. However, when the salt concentration was lowered to 50 mM NH4Cl, 5% cross-linking to the A site was detected, compared to 49% at the P site. Thus, a simple change in the ionic strength of the incubation mixture was able to alter the affinity labeling pattern of the ribosome.
The photobinding of [3H]8MOP to tRNA upon irradiation at 365 nm in the absence of O2 was determined by gel filtration. The maximum photobinding was found to be ca. 4 mol of 8MOP er mol of tRNA and 5FU-tRNA, with an overall quantum yield of 2.3 X 10(-3). The photobinding kinetics for 8MOP-tRNA showed an apparent induction period or sigmoidal kinetic curve, indicating a specific initial photobinding site on tRNA which was identified as 4-thiouridine at position 8 from the 5'-end of Escherichia coli tRNA. Photobinding of 8MOP to 5FU-tRNA proceeded without an apparent induction period. 8MOP-tRNA and 8MOP-5FU-tRNA adducts were characterized by absorption, fluorescence, and CD spectroscopy. A modified procedure was also developed to analyze the nucleoside composition in modified 8MOP-tRNA and 8MOP-5FU-tRNA. The results showed that 8MOP photochemically added mainly to pyrimidine bases. The photobinding of 8MOP changed the conformation (secondary in particular) of tRNA and inhibited aminoacyl-tRNA synthetase activity.
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While the Escherichia coli Su-3 (tyrT) tyrosine tRNA suppressor inserts only tyrosine at amber codons in E. coli, we show here that in Saccharomyces cerevisiae this tRNA inserts leucine and no significant amounts of any other amino acid. Thus, the E. coli tyrosine tRNA is functionally a leucine tRNA in yeast cytoplasm. This functional identity may correlate with a structural relationship between the E. coli tyrosine and yeast leucine tRNAs, which are both members of the uncommon type II class of tRNA structures. The results raise the possibility that in evolution a tRNA may be more closely related to a tRNA of different acceptor specificity, but of the same type class, than to one with the same amino acid specificity, but of a different type class.
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Binding of tRNA(Met/f) to the monomeric trypsin-modified methionyl-tRNA synthetase turns off the methionine-dependent isotopic ATP--PPi exchange. In the case of the dimeric native methionyltRNA synthetase, one anticooperatively bound tRNA(Met/f) inhibits the exchange by only 50%. These behaviours of tRNA do not require the integrity of the 3'-terminal adenosine. Esterification by methionine of the 3' end of tRNA reinforces the affinity of tRNA(Met/f)for the enzymes. In the case of the native enzyme, due to this effect, a second binding mode for methionyl-tRNA may be demonstrated through the isotopic exchange. This additional binding of tRNA corresponds to the expression of the anticooperatively blocked tRNA binding site. Methionine reverses competitively the reinforcing effect of the esterified methionyl moiety on tRNA binding. It is concluded that after esterification of tRNA, the aminoacyl residue still binds the enzyme, probably within the methionine activating site. The latter behaviour may account for the observation that excess methionine accelerates the aminoacylation turnover rate of tRNA(Met/f).
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