Call obligations in radiology residency: a survey.

RATIONALE AND OBJECTIVES: The authors evaluated the initial assignment of call responsibilities during residency, the effect on call obligations of the number of residents, and the differences between private and university programs and level 1 and non-level 1 trauma centers. MATERIALS AND METHODS: A survey was sent to all 203 diagnostic radiology residency programs accredited by the Accreditation Council for Graduate Medical Education. Chief residents at 21 institutions were surveyed by phone or in person. Directors of residency programs in the Graduate Medical Education Directory received the survey electronically. RESULTS: Responses were received from 99 (68 university, 31 private practice) of the 203 programs. Nine (9%) reported both a decreased number of residents and a subsequent increase in call obligations. First-year residents generally began to accept calls with a senior resident or alone at a median of 6 months, although 15 (48%) private practice programs required them to accept calls alone before this time. First-year residents at university programs (31%) were more likely to assume call duties during the first 6 months accompanied by a senior resident. Maximum time before 1st-year residents started going on call was 13 months. CONCLUSION: Call obligations remain a resident responsibility. University and private practice programs differ more than level 1 and non-level 1 trauma centers.

Location of putative binding and catalytic sites of NaeI by random mutagenesis.

Endonuclease NaeI is a prototype for an unusual group of type II restriction endonucleases that must bind two DNA recognition sequences to cleave DNA. The naeIR gene, expressed from a Ptac promotor construct, was toxic to Escherichia coli in the absence of NaeI-sequence specific methylases. The naeIR gene was mutagenized with N-methyl-N'-nitrosoguanidine; four classes of NaeI variants were isolated in the absence of protecting methylase activity. Class I variants (T60I, E70K) lacked detectable cleavage activity, but displayed good sequence-specific DNA binding. Class II variants (D95N, G141D) displayed 1-5% of the wild-type cleavage activity and normal DNA binding. Class III variants (G131E, G131R, G155D, G245E) displayed significantly attenuated cleavage and binding activities. Class IV variants (G197D, G214R/A219T, G236S, L241P, G245E, G245R, G250E, G270E) lacked both cleavage and binding activities. These results imply two amino acids (Thr-60, Glu-70) essential for catalysis. In addition, two domains are indicated in NaeI: one (Thr-60 to Gly-155) mediates substrate binding and catalysis, the other (Gly-197 to Gly-270) may mediate binding of the activating DNA sequence. Our results are compared with the active site residues of EcoRI, EcoRV, and BamHI.

Isolation of an SV40 induced sarcoma transformation associated antigen.

A transformation associated antigen was isolated from an SV40 induced hamster sarcoma by sequential silica gel column chromatography and preparative silica gel 60 thin layer chromatography after tissue extraction with chloroform:methanol (2:1, v/v). It migrated with an rf of 0.21 on silica gel 60 thin layer chromatography plates predeveloped and developed in chloroform:methanol:water:glacial acetic acid (10:10:1.5:0.5, v/v) and an rf of 0.27 on cellulose F254 thin layer chromatography plates developed in the same solvent system. Antigenicity was determined using a fluorescence probe cytotoxicity assay to measure inhibition of antibody mediated complement dependent damage to homologous cultured transformed cells. Although compositional analysis of this substance is not complete, it appears to be a polar lipid and would support the concept that transformation associated antigens may be gene plus substrate specific rather than strictly gene specific.