Many researchers have reported that obesity is a major risk factor for diabetes, cardiovascular diseases, several forms of cancer (such as breast, colon and prostate), pulmonary, osteoarticular and metabolic diseases in the past decades. Recently, the hypolipidemic and anti-obesity effects of green tea in animals and humans have slowly become a hot topic in nutritional and food science research. This review will up-date the information of the anti-obesity effects of green tea in human intervention and animal studies. During recent years, an increasing number of clinical trials have confirmed the beneficial effects of green tea on obesity. However, the optimal dose has not yet been established owing to the very different results from studies with a similar design, which may be caused by differences in the extent of obesity, dietary intake, physical activity intensity, the strength of subjects' compliance to test instruction, the genetic background of populations, body composition and dietary habits. Therefore, further investigations on a larger scale and with longer periods of observation and tighter controls are needed to define optimal doses in subjects with varying degrees of metabolic risk factors and to determine differences in beneficial effects among diverse populations. Moreover, data from laboratory studies have shown that green tea has important roles in fat metabolism by reducing food intake, interrupting lipid emulsification and absorption, suppressing adipogenesis and lipid synthesis and increasing energy expenditure via thermogenesis, fat oxidation and fecal lipid excretion. However, the exact molecular mechanisms remain elusive.

No abstract

DNA polymerase (Pol) is a newly identified member of the polymerase X family. The biological function of Pol is not known, although it has been speculated that human Pol may be a somatic hypermutation polymerase. To help understand the in vivo function of human Pol, we have performed in vitro biochemical analyses of the purified polymerase. Unlike any other DNA polymerases studied thus far, human Pol catalyzed frameshift DNA synthesis with an unprecedentedly high frequency. In the sequence contexts examined, ؊1 deletion occurred as the predominant DNA synthesis mechanism opposite the single-nucleotide repeat sequences AA, GG, TT, and CC in the template. Thus, the fidelity of DNA synthesis by human Pol was largely dictated by the sequence context. Human Pol was able to efficiently extend mismatched bases mainly by a frameshift synthesis mechanism. With the primer ends, containing up to four mismatches, examined, human Pol effectively realigned the primer to achieve annealing with a microhomology region in the template several nucleotides downstream. As a result, human Pol promoted microhomology search and microhomology pairing between the primer and the template strands of DNA. These results show that human Pol is much more prone to cause frameshift mutations than base substitutions. The biochemical properties of human Pol suggest a function in nonhomologous end joining and V(D)J recombination through its microhomology searching and pairing activities but do not support a function in somatic hypermutation.Many cellular processes require a DNA polymerase (Pol), including DNA replication, DNA repair, recombination, translesion DNA synthesis, and somatic hypermutation. Pol␣, Pol␦, Polε, and Pol␥ are replicative DNA polymerases in eukaryotes (16,29). Pol is a major polymerase required for DNA damage-induced mutagenesis (21,22). Pol is likely involved in repair of DNA interstrand cross-links (27). Pol, Pol, and Pol belong to the Y (UmuC) family of DNA polymerases and are involved in error-free and error-prone translesion synthesis opposite various DNA lesions (9,20,24,31).Pol␤ is a major repair synthesis polymerase during base excision repair in higher eukaryotes (17,33,36). Pol␤ and terminal deoxynucleotidyltransferase (TdT) are members of the DNA polymerase X family (13). TdT catalyzes nucleotide addition to DNA in a template-independent manner (3, 5). This enzyme is restricted to lymphoid tissues and functions during V(D)J recombination of the immunoglobulin genes and T-cell receptor genes (3,5,32). Most recently, the two newest members of the DNA polymerase X family, designated Pol and Pol, have been identified in humans (1, 8, 10). According to protein sequence comparisons, Pol is more closely related to Pol␤ while Pol is phylogenetically closer to TdT (1, 8). The biological functions of Pol and Pol remain to be defined. It has been speculated that Pol may play a role in meiosis (10) and that Pol may be a somatic hypermutation polymerase (8).V(D)J recombination and somatic hypermutation are two essential mechanis...

Abasic (AP) sites are major DNA lesions and are highly mutagenic. AP site-induced mutagenesis largely depends on translesion synthesis. We have examined the role of DNA polymerase eta (Poleta) in translesion synthesis of AP sites by replicating a plasmid containing a site-specific AP site in yeast cells. In wild-type cells, AP site bypass resulted in preferred C insertion (62%) over A insertion (21%), as well as -1 deletion (3%), and complex event (14%) containing multiple mutations. In cells lacking Poleta (rad30), Rev1, Polzeta (rev3), and both Poleta and Polzeta, translesion synthesis was reduced to 30%, 30%, 15% and 3% of the wild-type level, respectively. C insertion opposite the AP site was reduced in rad30 mutant cells and was abolished in cells lacking Rev1 or Polzeta, but significant A insertion was still detected in these mutant cells. While purified yeast Polalpha effectively inserted an A opposite the AP site in vitro, purified yeast Poldelta was much less effective in A insertion opposite the lesion due to its 3'-->5' proofreading exonuclease activity. Purified yeast Poleta performed extension synthesis from the primer 3' A opposite the lesion. These results show that Poleta is involved in translesion synthesis of AP sites in yeast cells, and suggest that an important role of Poleta is to catalyze extension following A insertion opposite the lesion. Consistent with these conclusions, rad30 mutant cells were sensitive to methyl methanesulfonate (MMS), and rev1 rad30 or rev3 rad30 double mutant cells were synergistically more sensitive to MMS than the respective single mutant strains.

The current study investigated the effects of green tea polyphenols (GTPs) on lipid metabolism and its mechanisms using broiler chickens (Gallus gallus domesticus). A total of 36 male chickens (35 days old) had been subjected to an oral administration of GTPs at a dosage of 0, 50 (low), and 100 (high) mg/kg of body weight for 20 days. Our results showed that GTPs significantly decreased the abdominal and subcutaneous fat masses of broilers and reduced the serum triglyceride, total cholesterol, and low-density lipoprotein cholesterol levels compared to those of the control. Furthermore, the expression levels for lipid anabolism genes were significantly downregulated, while the expression levels of fat transportation and catabolism-related genes, carnitine palmitoyl transferase I (CPT-I), acyl-CoA oxidase 1 (ACOX1), and peroxisome proliferator-activated receptor-α (PPARα) in liver, adipose triglyceride lipase (ATGL) in abdominal fat, and lipoprotein lipase (LPL) in skeletal muscles, were notably upregulated. Our data have revealed that GTPs alleviate obesity and serum lipid levels in broiler chickens by suppressing fatty acid synthesis and stimulating lipolysis.