No abstract

Since the proposition of introns-early hypothesis, although many studies have shown that most eukaryotic ancestors possessed intron-rich genomes, evidence of intron existence in genomes of ancestral bacteria has still been absent. While not a single intron has been found in all protein-coding genes of current bacteria, analyses on bacterial genes horizontally transferred into eukaryotes at ancient time may provide evidence of intron existence in bacterial ancestors. In this study, a bacterial gene encoding capsule biosynthesis protein CapI was found in the genome of sea anemone, Nematostella vectensis. This horizontally transferred gene contains a phase 1 intron of 40 base pairs. The nucleotides of this intron have high sequence identity with those encoding amino acids in current bacterial CapI gene, indicating that the intron and the amino acid-coding nucleotides are originated from the same ancestor sequence. Moreover, 5′-splice site of this intron is located in a GT-poor region associated with a closely following AG-rich region, suggesting that deletion mutation at 5′-splice site has been employed to remove this intron and the intron-like amino acid-coding nucleotides in current bacterial CapI gene are derived from exonization. These data suggest that bacterial CapI gene contained intron(s) at ancient time. This is the first report providing the result of sequence analysis to suggest possible existence of spliceosomal introns in ancestral bacterial genes. The methodology employed in this study may be used to identify more such evidence that would aid in settlement of the dispute between introns-early and introns-late theories.

With the computational fluid dynamics (CFD) software POLY-FLOW, simplified models and numerical simulation are conducted on the single screw pin unit and the single screw unit. Comparative analysis is carried out on the mixing properties of these two mixing units under vibration-less and vibrant operating conditions. It is found that in comparison to the single screw mixing unit, the pin unit has longer residence time, smaller segregation scale, larger mixing index and higher instantaneous efficiency of stretching; it also possesses better diffluence and rearrangement, flow state, fluidity and plasticization performance for the polymer melt particles under vibration field. This provides references for the design and research of new type mixing device. INTRODUCTIONMixing may be used for a number of different reasons, which include blending of ingredients, facilitation of chemical reactions, addition of energy in order to create or break molecular bonds, incorporation of air, etc. [1] . And mixing is of great importance for many new properties in composite materials. Ming-Wen Wang [2] has found that using meltmixing process or in situ polymerization leads to better dispersion effect on composite materials. Anoop Anand [3] investigated the stabilized aqueous dispersion of SWNTs mixed with NR latex and the effect of nanofiller on the flow properties of NR latex and found that casting the compounded latex followed by curing gave good quality composite films with significantly improved mechanical properties.Experiments [4] show that when chitosan and sodium alginate were mixed in weight ratio of 5:1, a polyelectrolyte complex film was formed and exhibited better thermal stability and stronger control ability over drug release. With the rapid development and the increasing species of polymer blending modification, it attracts much attention to design and research new mixing equipments [5] . Up to

Taq DNA polymerase is one of the most commonly thermostable DNA polymerases in molecular biological researches, which shares its basic characters with others of the family, thereby its purifying strategy could be used not only in itself production but also in the extraction of the others as a reference. At present, the protocols reported for large scale preparation of Taq DNA are high cost, so a cheaper method was described here. In this protocol, by heat denaturation, ammonium sulfate precipitation and cation exchange chromatography of 724 resin, about 18 g powder of Na form resin could recover about 27.07 mg of Taq enzyme. The total activity and specific activity were approximately 2.2 × 10⁵ U and 8131.98 U/mg. The total yield was about 48.92% with 59.35 of purification folds. Analysis of quality of purified enzyme indicated that only one protein 94 kDa was identified against SDS-PAGE and the remnant of DNA nuclease was not detected. For PCR reaction, The amplification ability of purified Taq polymerase was not different from that of the commercially avail-able ones. This method reported in the present study is effective and low cost, making it suitable for general purification in laboratories or business production.