The positive impact of conservation action

Governments recently adopted new global targets to halt and reverse the loss of biodiversity. It is therefore crucial to understand the outcomes of conservation actions. We conducted a global meta-analysis of 186 studies (including 665 trials) that measured biodiversity over time and compared outcomes under conservation action with a suitable counterfactual of no action. We find that in two-thirds of cases, conservation either improved the state of biodiversity or at least slowed declines. Specifically, we find that interventions targeted at species and ecosystems, such as invasive species control, habitat loss reduction and restoration, protected areas, and sustainable management, are highly effective and have large effect sizes. This provides the strongest evidence to date that conservation actions are successful but require transformational scaling up to meet global targets.

Tubal pregnancy associated with a benign cystic teratoma of the fallopian tube. A case report

A benign teratoma of the fallopian tube occurred in association with a tubal pregnancy. This rare finding should be considered when two masses are present within a fallopian tube.

Physical chemical studies of the structure and function of DNA binding (helix-destabilizing) proteins

Binding of proteins to DNA is fundamental to the mechanisms of replication, recombination and gene expression. The specific molecular features of DNA recognized by complementary features of the three-dimensional structure of the DNA binding proteins are under intensive investigation. Two large classes of DNA binding proteins have emerged. One class includes enzymes such as the RNA polymerases and restriction endonucleases and the nonenzymatic repressor proteins which recognize unique sequences present in only one or a few copies per genome. A second group is made up of non-sequence-specific DNA binding proteins which bind to DNA at high density and modulate subsequent enzymatic transformations of the DNA. Among the latter group are those proteins originally termed "unwinding proteins", which have in common a higher affinity for single-stranded than for double-stranded DNA and thus promote the melting of double-stranded DNA. They are better termed helix-destabilizing proteins to distinguish them from the enzymes which "unwind" the helix by making and breaking phosphodiester bonds. Because the helix-destabilizing proteins form complexes with all single-stranded DNA regardless of base sequence, the molecular details of complex formation have been much more accessible to direct physicochemical measurements. Structural conclusions derived with techniques which include chemical modification, ultraviolet spectroscopy, circular dichroism, NMR, and X-ray diffraction will be reviewed. The following proteins will be discussed in detail; the gene 32 protein of bacteriophage T4, the gene 5 protein from bacteriophage fd, and the helix-destabilizing protein from E. coli. The largest amount of specific structural information is available for the gene 5 protein and specific models for this protein and its complexes with DNA based on NMR and X-ray diffraction data are presented. A number of other helix-destabilizing proteins from both prokaryotes and eukaryotes have been described and a survey of these will be given. Some of the basic molecular features of DNA-protein interactions emerging from studies of the helix-destabilizing proteins are likely to be shared by the more highly specific binding proteins like the RNA polymerases and repressors. Properties of some of these more complex systems which suggest this will be discussed.

T7 RNA polymerase: promoter structure and polymerase binding

The sequences of two promoters recognized by the phage-specificied T7 RNA polymerase are presented. The two are identical in sequence but for one base pair from the initiation point (as determined by the 5' sequence of the transcripts), denoted +1, to position -15. The common : formula: (see text), sequence also includes a region of hyphenated twofold symmetry indicated by the boxes, with the twofold axis as the center of the six base-pair box. The heavy line indicates the extent of homology. The first promoter (A) is demonstrated to lie within gene 1, the gene for the polymerase itself, and 40 bases into the message transcribed from this promoter is found the R Nase III site separating genes 1 and 1.1. Binding of T7 RNA polymerase to these promoters is associated with a hyperchromic blue shift of the base chromophores consistent with partial melting of the base pairs at the promoter. Binding of T7 RNA polymerase to these promoters disappears at low pH and low temperature and is accompanied by a consequent loss of polymerase activity. The pH dependence of the binding step is adequately described by a single pK of 7.0. Polymerase catalytic activity, but not promoter binding, requires a single free sulfhydryl group of the enzyme with a pKa of approximately 7.8.

Structure of a promoter for T7 RNA polymerase

We have determined the nucleotide sequence of a Hpa II restriction fragment of the phage T7 DNA containing a promoter for the phage-specified RNA polymerase. (Hpa II is a restriction endonuclease from Haemophilus parainfluenzae.) Mapping of the Hpa II restriction fragments on the T7 genome shows this promoter to be the second of tandem promoters separated by approximately 170 base pairs that begin transcription by the T7 RNA polymerase at approximately 15% of the genome. Features of the sequence involved in recognition by the T7 RNA polymerase are discussed and include the following region of hyphenated 2-fold symmetry (boxed regions are related through a 2-fold axis of symmetry at the center of the sequence shown). (See article). This sequence includes the initiation site, since the message transcribed from this fragment begins pppG-G-G-A. Combination of our results with work of others has permitted this fragment to be mapped at the junction of T7 genes 1 and 1.1. The RNA transcribed from this fragment begins within gene 1 and contains the RNase III cleavage site that lies between genes 1 and 1.1. This sequence is compared to other processing sites in T7 early message.

T7 RNA polymerase: conformation, functional groups, and promotor binding

Circular dichroic spectra of T7 RNA polymerase show minima at 222 nm ([theta]m=-7.9 X 10(3) deg cm2/dmol) and 208 nm ([theta]m =-7.55 X 10(3) deg cm2/dmol) and a maximum at 193 nm ([theta]m = 1.2 X 10(4) deg cm2/dmol). The small mean residue ellipticity above 200 nm indicates that the secondary structure contains approximately 12% alpha helix. The secondary structure is unaltered by high salt, glycerol, -SH reagents, nitration of tyrosyl residues, and chelating agents. Binding of the native enzyme to [32P]T7 DNA has been measured by the retention of the protein-[32P]DNA complexes on nitrocellulose filters. At 37degrees T7 RNA polymerase binds to its promoters in the absence of NTP's. Binding and catalytic activity are both abolished at 0degree. Binding of the initiating [gamma-32P]GTP can also be detected by the filter binding assay. Native T7 RNA polymerase is inactivated by reaction with 1 mol of 5,5'-dithiobis(2-nitrobenzoic acid) (Nbs2) or 1 mol of [14C]iodoacetamide. The latter reaction is blocked by Nbs2 suggesting that a single -SH group is required for activity. Alkylation of the -SH group does not alter binding of the enzyme to the DNA template, but modifies the binding of GTP to the enzyme. Nitration of approximately4 surface tyrosyl residues of the protein prevents binding to T7 DNA. The restriction endonuclease, Hpa II, cuts T7 DNA into approximately40 fragments and reduces total RNA synthesis by T7 RNA polymerase by 70%. Fragmentation of the DNA template by Hpa II does not alter the rate of RNA chain initiation by T7 polymerase, and restriction fragments accounting for approximately25% of the T7 DNA still bind tightly to the enzyme. Thus the T7 RNA polymerase promoters remain intact on the restriction fragments. Gel electrophoresis of the transcription products, using restriction fragments as templates, show that of the seven in vitro transcripts produced by T7 RNA polymerase from whole T7 DNA, only the smallest (representing the last 1.5% of the genome) is transcribed from Hpa II fragments. The remaining transcripts are replaced by six new and much shorter mRNA's. The DNA fragments containing the promoters for these mRNA's have been removed from the fragment mix by binding them to the enzyme and retaining the complexes on nitrocellulose filters.