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S Rippel

Publications and source records attributed to S Rippel.

4 recordsLinked to original sources
PubMed2001

Biochemical analysis of the eIF2beta gamma complex reveals a structural function for eIF2alpha in catalyzed nucleotide exchange.

Eukaryotic translation initiation factor eIF2 is a heterotrimer that binds and delivers Met-tRNA(i)(Met) to the 40 S ribosomal subunit in a GTP-dependent manner. Initiation requires hydrolysis of eIF2-bound GTP, which releases an eIF2.GDP complex that is recycled to the GTP form by the nucleotide exchange factor eIF2B. The alpha-subunit of eIF2 plays a critical role in regulating nucleotide exchange via phosphorylation at serine 51, which converts eIF2 into a competitive inhibitor of the eIF2B-catalyzed exchange reaction. We purified a form of eIF2 (eIF2betagamma) completely devoid of the alpha-subunit to further study the role of eIF2alpha in eIF2 function. These studies utilized a yeast strain genetically altered to bypass a deletion of the normally essential eIF2alpha structural gene (SUI2). Removal of the alpha-subunit did not appear to significantly alter binding of guanine nucleotide or Met-tRNA(i)(Met) ligands by eIF2 in vitro. Qualitative assays to detect 43 S initiation complex formation and eIF5-dependent GTP hydrolysis revealed no differences between eIF2betagamma and the wild-type eIF2 heterotrimer. However, steady-state kinetic analysis of eIF2B-catalyzed nucleotide exchange revealed that the absence of the alpha-subunit increased K(m) for eIF2betagamma.GDP by an order of magnitude, with a smaller increase in V(max). These data indicate that eIF2alpha is required for structural interactions between eIF2 and eIF2B that promote wild-type rates of nucleotide exchange. We suggest that this function contributes to the ability of the alpha-subunit to control the rate of nucleotide exchange through reversible phosphorylation.

Catalysis↗
PubMed2001

Minimum requirements for the function of eukaryotic translation initiation factor 2.

Eukaryotic translation initiation factor 2 (eIF2) is a G protein heterotrimer required for GTP-dependent delivery of initiator tRNA to the ribosome. eIF2B, the nucleotide exchange factor for eIF2, is a heteropentamer that, in yeast, is encoded by four essential genes and one nonessential gene. We found that increased levels of wild-type eIF2, in the presence of sufficient levels of initiator tRNA, overcome the requirement for eIF2B in vivo. Consistent with bypassing eIF2B, these conditions also suppress the lethal effect of overexpressing the mammalian tumor suppressor PKR, an eIF2alpha kinase. The effects described are further enhanced in the presence of a mutation in the G protein (gamma) subunit of eIF2, gcd11-K250R, which mimics the function of eIF2B in vitro. Interestingly, the same conditions that bypass eIF2B also overcome the requirement for the normally essential eIF2alpha structural gene (SUI2). Our results suggest that the eIF2betagamma complex is capable of carrying out the essential function(s) of eIF2 in the absence of eIF2alpha and eIF2B and are consistent with the idea that the latter function primarily to regulate the level of eIF2.GTP.Met-tRNA(i)(Met) ternary complexes in vivo.

Cell Division↗
PubMed1994

Effect of the introduction of dietary sucrose on metabolic control in children and adolescents with type I diabetes.

The effect of sucrose in the diet of children and adolescents with type I diabetes on long-term metabolic control was studied. For a mean observation period of 83 (range 42-127) days, a diet containing 5% of total calories as refined sugar was recommended to 11 children (group A, mean age 15.0, SD 5.4 years), while another 13 children remained on their usual 'sucrose-free' diet (group B, mean age 16.0, SD 5.7 years). The mean observation period in this group was 77 (41-103) days. All children had a dietary assessment at baseline and at follow up using a 7-day food record. At baseline, sucrose intake as a proportion of total daily calories was similar in the two groups (group A 1.4, SD 1.9% vs group B 2.0, SD 2.3%; P = 0.5). At follow-up, sucrose intake increased significantly in group A (5.1, SD 2.5%; P = 0.0008) but not in group B (2.7, SD 3.3%; P = 0.5). Metabolic control assessed by haemoglobin level (HbA1c) was not different between the groups at baseline (group A 8.5, SD 1.2 vs group B 8.8, SD 1.8%; P = 0.7) nor at follow-up (9.1, SD 1.4 vs 9.0, SD 2.5%; P = 0.9). Within group A, the individual change in HbA1c correlated with the individual change in sucrose intake (r = 0.61, P = 0.05), this correlation being strongly influenced by two individuals with an increase in sucrose consumption substantially exceeding 5%. Percentage intake of protein, carbohydrate and fat did not change significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗