Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position

I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages, and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types, species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility. To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and land bridge islands, but at much smaller space and time scales. Received: 6 December 1996 / Accepted: 10 December 1996     

Sp1 and Sp3 regulate basal transcription of the survivin gene

Survivin, a unique member of the inhibitor of apoptosis protein family, is overexpressed in many cancers and considered to play an important role in oncogenesis. In this study, we cloned and identified the proximal 269 bp promoter of survivin gene, which exhibited strong promoter activity in HeLa cells. The TATA-less, GC-rich promoter contains 7 putative binding sites for Sp1, two of which (one at position -148 to -153, the other at position -127 to -140) are essential in regulating basal survivin promoter activity. Not only Sp1 but also Sp3 can activate the survivin promoter, which were proven by EMSA, blocking Sp1 or Sp3 using RNAi or mithramycin treatment of HeLa cells, and overexpression of Sp1 or Sp3. Our results collectively suggest that Sp1 cooperates with Sp3 to regulate survivin promoter activity.     

Isolation of the origin of replication of the IncW-group plasmid pSa

The origin of replication of the IncW plasmid pSa has been cloned and the function of this origin in Escherichia coli examined. A 1.9-kb region of DNA is required for efficient autonomous replication, and a 0.47-kb fragment within this region can initiate replication only in the presence of an autonomously replicating derivative of pSa. An Mr 35,000 protein (repA) is encoded adjacent to the origin and is required for efficient initiation of replication. The derivatives examined provide information suggesting a direct role of partition factors in plasmid replication and incompatibility.     

Psb30 contributes to structurally stabilise the Photosystem II complex in the thermophilic cyanobacterium Thermosynechococcus elongatus

A deletion mutant that lacks the Psb30 protein, one of the small subunits of Photosystem II, was constructed in a Thermosynechococcus elongatus strain in which the D1 protein is expressed from the psbA₃ gene (WT*). The ΔPsb30 mutant appears more susceptible to photodamage, has a cytochrome b₅₅₉ that is converted into the low potential form, and probably also lacks the PsbY subunit. In the presence of an inhibitor of protein synthesis, the ?Psb30 lost more rapidly the water oxidation function than the WT* under the high light conditions. These results suggest that Psb30 contributes to structurally and functionally stabilise the Photosystem II complex in preventing the conversion of cytochrome b₅₅₉ into the low potential form. Structural reasons for such effects are discussed.