Training delays reduce the choose-short effect with keylight, but not with food, duration samples in pigeons

Pigeons were trained to match 2- and 8-s food samples. The delay on training trials was either 0s (group 0sF), 5s (group 5sF), or varied between 2 and 8s (M=5s, group 5sV). Testing at a delay that exceeded the training delay by 15s in each group revealed a robust choose-short effect in each group. The same pigeons then reacquired a previously trained matching task involving 2- and 8-s keylight samples. Different comparison stimuli were used on food-sample and keylight-sample trials. The delay on training trials was the same on both food- and keylight-sample trials. Extended-delay testing revealed a robust choose-short effect in all three groups when the durations were conveyed by food presentations, but only group 0sF revealed a choose-short effect when the durations were conveyed by keylight presentations. Hence, training with a nonzero delay, whether fixed or variable, reduces the choose-short effect with keylight durations but not with food durations. It was concluded that at least some of the psychological processes mediating performance differ as a function of the event that conveys the duration.     

Shiga toxins even when different are encoded at identical positions in the genomes of related temperate bacteriophages

The nucleotide sequence of an 11,142-bp region including the stx ₂ operon in the genome of the temperate bacteriophage 933W in the EDL933 strain of Escherichia coli O157 was determined and compared to the respective regions derived from other lambdoid bacteriophages. In phage 933W, a region of ORFs interlinked by overlapping start-stop codons (ATGA) was detected preceding the toxin gene. These ORFs show a high degree of sequence identity to genes of the nin region of phage λ. Immediately downstream of these nin genes we identified an ORF that may code for an antiterminator similar to the λ Q protein. It is concluded that toxin expression is directly associated with the initiation of cell lysis. Downstream of the stx ₂ operon we identified an ORF that is homologous to the holin gene S of bacteriophage PA-2. PCR primers were designed, which, based on a comparison of the phage sequences, appeared to be common to both stx ₁ - and stx ₂ -harbouring phages. However, only seven of the 22 STEC strains investigated from serogroups O157, O26, O103 and O111 yielded the expected PCR amplification product. The data reported here may be useful in developing new strategies for inhibiting the expression of Stx and for developing universal diagnostic primers for use in tracking the origin and evolution of Shiga toxins and the phages that carry them. Received: 24 February 1999 / Accepted: 7 September 1999     

Collagen matrix deposition is dramatically enhanced in vitro when crowded with charged macromolecules: the biological relevance of the excluded volume effect

The excluded volume effect (EVE) rules all life processes. It is created by macromolecules that occupy a given volume thereby confining other molecules to the remaining space with large consequences on reaction kinetics and molecular assembly. Implementing EVE in fibroblast culture accelerated conversion of procollagen to collagen by procollagen C-proteinase (PCP/BMP-1) and proteolytic modification of its allosteric regulator, PCOLCE1. This led to a 20-30- and 3-6-fold increased collagen deposition in two- and three-dimensional cultures, respectively, and creation of crosslinked collagen footprints beneath cells. Important parameters correlating with accelerated deposition were hydrodynamic radius of macromolecules and their negative charge density.