Therapeutic angiogenesis is likely to require the administration of factors that complement each other. Activation of the receptor tyrosine kinase (RTK) Flk1 by vascular endothelial growth factor (VEGF) is crucial, but molecular interactions of other factors with VEGF and Flk1 have been studied to a limited extent. Here we report that placental growth factor (PGF, also known as PlGF) regulates inter- and intramolecular cross talk between the VEGF RTKs Flt1 and Flk1. Activation of Flt1 by PGF resulted in intermolecular transphosphorylation of Flk1, thereby amplifying VEGF-driven angiogenesis through Flk1. Even though VEGF and PGF both bind Flt1, PGF uniquely stimulated the phosphorylation of specific Flt1 tyrosine residues and the expression of distinct downstream target genes. Furthermore, the VEGF/PGF heterodimer activated intramolecular VEGF receptor cross talk through formation of Flk1/Flt1 heterodimers. The inter- and intramolecular VEGF receptor cross talk is likely to have therapeutic implications, as treatment with VEGF/PGF heterodimer or a combination of VEGF plus PGF increased ischemic myocardial angiogenesis in a mouse model that was refractory to VEGF alone.

A number of mRNAs in plant mitochondria contain inverted repeats at their 3'-termini. These have been discussed as potential transcription terminators or, alternatively, as post-transcriptional processing and stability signals of longer precursor RNAs. In vitro transcription in a pea mitochondrial lysate now shows that transcription proceeds almost unimpeded through these inverted repeat structures. To investigate their potential function in mRNA processing, we developed an in vitro processing system from pea mitochondria. This in vitro system correctly processes synthetic precursor mRNAs containing the pea atp9 double stem-loop structure, yielding the same 3'-termini observed in vivo. Analysis of the in vitro-generated products and of the processivity of the reaction suggests exonucleolytic degradation up to the stem-loop. The inverted repeat structures found at the 3'-termini of mRNAs in plant mitochondria are thus recognized as processing and most likely also stabilizing signals in transcript maturation, but do not terminate transcription.

The coordinated activation of both VEGFR-1 and VEGFR-2 represents a more potent arteriogenic stimulus compared to the isolated activation of either one of these two receptors. These data imply that the activation of both monocytes and endothelial cells is necessary to obtain a maximal VEGF-induced activation of arteriogenesis.

There was a lower proportion of subjects with an on-study relapse in natalizumab-treated patients, particularly in those with a more active disease at study entry. Larger ongoing phase III studies will allow more definitive investigation of these preliminary subgroup findings.

The nucleotide requirements of mitochondrial promoters of dicot plants were studied in detail in a pea in vitro transcription system. Deletions in the 5 regions of three different transcription initiation sites from pea, soybean, and Oenothera identified a crucial AT-rich sequence element (AT-Box) comprising nucleotide positions ؊14 to ؊9 relative to the first transcribed nucleotide. Transversion of the AT-Box sequence to complementary nucleotide identities results in an almost complete loss of promoter activity, suggesting that primary structure rather than a simple accumulation of adenines and thymidines in this region is essential for promoter activity. This promoter segment thus appears to be involved in sequence specific binding of a respective protein factor(s) rather than merely loosening and melting the DNA helix during or for an initiation event. Manipulation of nucleotide identities in the 3 portion of the pea atp9 promoter and the respective 3-flanking region revealed that essential sequences extend to positions ؉3/؉4 beyond this transcription start site. Efficient transcription initiation at an 18-base pair promoter sequence ranging from nucleotide positions ؊14 to ؉4 integrated into different sequence contexts shows this element to be sufficient for autonomous promoter function independent of surrounding sequences.The established endosymbiont hypothesis describes mitochondria and chloroplasts as remnants of bacteria-like progenitors, which penetrated the original eukaryote 1.5 and 1 billion years ago (1). The prokaryotic origin of the organellar DNAs implies that cis-elements engaged in the expression of the organellar genetic information might be similar to the respective control structures of modern bacteria. Such a similarity is indeed found in chloroplasts, where several components of the genetic system show a close structural and functional relationship to their prokaryotic counterparts (2). Many chloroplast promoters for instance resemble the Ϫ10/Ϫ35-type promoters of contemporary prokaryotes. These promoters serve as ciselements for a largely chloroplast encoded eubacteria-like RNA polymerase. Another, nuclear encoded polymerase initiates transcription at a second less well described class of promoters (3-6). This latter enzyme is of the bacteriophage-like single subunit type, a class of polymerases that also includes the RNA polymerases in mitochondria of animals, fungi, and plants (7-9). These enzymes bind to promoters in close spatial relationship to transcription initiation sites.In mitochondria of Saccharomyces cerevisiae a 9-base-pair-long highly conserved cis-element is found at each of the about 20 transcription initiation sites. This nonanucleotide motif autonomously supports efficient transcription initiation in vitro, with enhanced promoter activity depending on the presence of a purine at position ϩ2 and a pyrimidine at ϩ3. In Xenopus laevis mitochondria an eight-nucleotide-long cis-element drives bi-directional transcription initiation at two different locations. A 15-bp 1 consen...