The origin of interspersed repeats in the human genome

Over a third of the human genome consists of interspersed repetitive sequences which are primarily degenerate copies of transposable elements. In the past year, the identities of many of these transposable elements were revealed. The emerging concept is that only three mechanisms of amplification are responsible for the vast majority of interspersed repeats and that with each autonomous element a number of dependent non-autonomous sequences have co-amplified.     

Anomalous Cases of Conjugation and Spontaneous Autogamy in Stylonychia mytilus: A Note on the Asexuality of Early Conjugants

Four types of anomalous conjugation were documented in Stylonychia mytilus. Type I pairs were formed between mates of different sizes. These pairs exhibited an abnormal site of fusion in at least one of the mates, and the mates might face each other ventrally throughout conjugation instead of the normal side-by-side position. Type I pairs underwent sexual nuclear development and proceeded with the first cortical reorganization as in normal conjugants. Type II involved pairing at the anterior ends of mates with ventral surfaces facing the same direction. These pairs also underwent sexual nuclear development. Hence, aberrant orientation of the mates, and also ectopic sites of cytoplasmic fusion, if extensive, would permit sexual development. Type III pairs were united ventral-to-ventral with their anterior-left sides at the adoral zone of membranelles, and remained as such throughout conjugation. In these pairs, nuclear and cortical events were typical of the asexual development of physiological reorganization. In Type IV pairs, one mate of the pair possessed a fission furrow and developed two sets of ciliature typical of binary fission, while the other mate might undergo physiological reorganization or binary fission. Type III and Type IV pairs thus reveal the asexual state of early conjugants, which can pursue either one of the two modes of asexual cortical reorganization; these cases reinforce the notion of overlap of asexual and sexual cycles during conjugation of hypotrichs. Spontaneous autogamy was documented for the first time for this genus. The autogamonts proceeded with nuclear development and with the first cortical reorganization. Some probably underwent second and third reorganizations, as in conjugants, but accompanied by abnormalities, particularly in the stages beyond fertilization. Post-autogamous clones were nonviable except for one dubious case.     

Fluorescence of tryptophan residues in firefly luciferases and enzyme--substrate complexes

Quenching of tryptophan fluorescence of Luciola mingrelica (single tryptophan residue, Trp-419) and Photinus pyralis (two tryptophan residues, Trp-417 and Trp-426) luciferases with different quenchers (I-, Cs+, acrylamide) was studied. The conserved Trp-417(419) residue was shown to be not accessible to charged particles, and positively and negatively charged amino acid residues are located in close vicinity to it. We found previously unreported effective energy transfer from this tryptophan to luciferin during the quenching of the tryptophan fluorescence. The distance between the luciferin molecule and Trp-417(419) was calculated: 11-15 and 12-17 A for P. pyralis and L. mingrelica luciferases, respectively. The role of the conserved Trp residue in the catalysis is discussed. ATP and AMP are also quenchers of the tryptophan fluorescence of the luciferases. In this case, an allosteric mechanism of the interaction of Trp-417(419) with an excess of ATP (AMP) is proposed.     

犁头霉11α-羟基化制备16β-甲基-11α,17α,21-三羟基孕甾-1,4-二烯-3,20-二酮

选育到一株对16β-甲基,17α,21-二羟基孕甾-1,4-二烯-3,20-二酮(Ⅱa)11α-羟基化活性强的犁头霉A28菌株,并发现底物21-乙酰化(Ⅱb)可明显提高11α-羟基化的能力.在适宜的转化条件下,Ⅱb投料浓度0.5%,产物16β-甲基-11α,11α,21-三羟基孕甾-1,4-二烯-3,20-二酮(Ⅲ)收率为73%,结构经波谱分析确认.     

Bioluminescent assay of total bacterial contamination of raw milk]

A rapid (30-35 min) bioluminescence assay of total bacterial contamination (TBC) of raw milk was optimized. This method includes incubation of milk samples in the presence of Neonol-10 and medical purity grade pancreatin with further removal of nonbacterial ATP by filtration through a membrane filter, cell disruption by treatment with dimethyl sulfoxide, and measurement of ATP concentration in a reaction with the bioluminescent reagent Immolum. The TBC detection threshold is 0.5 x 10(5) colony-forming units (CFU) per ml milk. Coefficients of correlation between the standard plate count method and bioluminescence assay (R) and residual standard deviations (Sxy) in raw milk samples (n = 140) were 0.83 and 0.54, respectively. In sterilized milk samples artificially contaminated with pure cultures of the main representatives of milk microflora (coli-forms, Staphylococcus aureus, Streptococcus thermophilus, and Streptococcus group D), these values were 0.89-0.99 and 0.09-0.29, respectively. The specific content of ATP was found to be (0.8 +/- 0.1) x 10(-18) mol/CFU in coli-forms; (12.0 +/- 8.1) x 10(-18) mol/CFU in S. aureus; (35.2 +/- 16.9) x 10(-18) mol/CFU in S. thermophilus; and (42.5 +/- 1.3) x 10(-18) in Streptococcus group D.     

Multicellular compartmentation of catharanthus roseus alkaloid biosynthesis predicts intercellular translocation of a pathway intermediate

In situ RNA hybridization and immunocytochemistry were used to establish the cellular distribution of monoterpenoid indole alkaloid biosynthesis in Madagascar periwinkle (Catharanthus roseus). Tryptophan decarboxylase (TDC) and strictosidine synthase (STR1), which are involved in the biosynthesis of the central intermediate strictosidine, and desacetoxyvindoline 4-hydroxylase (D4H) and deacetylvindoline 4-O-acetyltransferase (DAT), which are involved in the terminal steps of vindoline biosynthesis, were localized. tdc and str1 mRNAs were present in the epidermis of stems, leaves, and flower buds, whereas they appeared in most protoderm and cortical cells around the apical meristem of root tips. In marked contrast, d4h and dat mRNAs were associated with the laticifer and idioblast cells of leaves, stems, and flower buds. Immunocytochemical localization for TDC, D4H, and DAT proteins confirmed the differential localization of early and late stages of vindoline biosynthesis. Therefore, we concluded that the elaboration of the major leaf alkaloids involves the participation of at least two cell types and requires the intercellular translocation of a pathway intermediate. A basipetal gradient of expression in maturing leaves also was shown for all four genes by in situ RNA hybridization studies and by complementary studies with dissected leaves, suggesting that expression of the vindoline pathway occurs transiently during early leaf development. These results partially explain why attempts to produce vindoline by cell culture technology have failed.     

Elaboration of the method for immunocytochemical studying cytokinin-binding protein CBP70 localization in maize seedling tissues

Some approaches for the elaboration of the method for immunocytochemical detection of labile protein on sections prepared from maize (Zea mays L.) seedling tissues are outlined. The effects of severe chemical reagents applied during tissue pretreatment (fixatives, inhibitors of endogenous enzymes, solutions blocking nonspecific antibody binding) on labile protein immunoreactivity in extracts were assessed in preliminary experiments. The procedure was elaborated with a triple control, which provided for the lowest background staining on plant tissue sections and the high level of antibody specific binding.     

Visual stabilization of the eyes in primates

Observers moving through a texture three-dimensional world experience potentially confusing patterns of optic flow. Recent experiments on monkeys and humans have revealed the existence of rapid, yet cortically mediated, reflex eye movements that automatically single out images in the plane of fixation for stabilization and ignore images that are nearer or further.     

Generation of scFv phages specific to Staphylococcus enterotoxin C1 by panning on related antigens

A method for generation of highly specific miniantibodies within the phage particle has been developed and used to produce antibodies against Staphylococcus enterotoxin type C1. Under successive panning of the non-immune phage miniantibody (scFv) library with enterotoxins SE (types A, B, C1, D, E, G and I) adsorbed on the plate surface, we generated 11 individual phage clones to Staphylococcus enterotoxin type C1. Five of them interacted specifically only with SEC1 and had no cross-reactions with the other enterotoxins.Key words: scFv, phage display, antibody specificity, Staphylococcus aureus enterotoxins