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Specifications grading is a relatively recent approach to assessing student learning. In this approach, students make progress toward completion of a course by demonstrating mastery of specific skills or material. The assessment tools are short, frequent exercises that can be attempted multiple times until mastered. This contrasts with the traditional, exam-based assessment of student learning. There are multiple benefits to the specifications grading-based strategy, including reduced test anxiety, better knowledge retention, and increased flexibility. In this study, specifications grading was implemented into an upper-level biochemistry course at a private, liberal arts university. The student cohort consisted almost exclusively of junior and senior biochemistry, biology, and chemistry majors. Students earned points for demonstrating mastery on each of 12 short quizzes in addition to points earned from laboratory exercises and on the cumulative final exam. Student attitudes were assessed using three surveys that were administered at the beginning, middle, and end of the course. The survey results indicated that the students had overall favorable opinions of the specifications grading approach and its use in this course. A comparison of student performance on the quizzes to their performance on the final exam showed that the students learned and retained the course material. Combining the survey and performance data, we demonstrated that the students' perceptions of their learning correlated well with their performances on the specifications grading tools. Together, these results indicated that specifications grading is an effective approach to assessing student learning and to maintaining student enthusiasm in an upper-level biochemistry course.

G-wires are formed by the spontaneous self-assembly of the telomeric DNA oligonucleotide S'-G4T2G4-3' (Tet 1.5). The application of Gel electrophoresis resolves the G-wires into ladder patterns. The Tet 1.5 exhibits parallel four-stranded structure, which is stable due to the guanine tetrads. The Tet 1.5 has characteristics similar to the G4-DNA and its self-association is noncovalent in nature. The presence of sodium and potassium ions enhance the formation of G-wires. The study of G-wires may provide information about G-rich nucleic acids.

Rad51p, the eukaryotic homolog of the prokaryotic recA protein, catalyzes strand exchange between single- and double-stranded DNA and is involved in both genetic recombination and double-strand break repair in the ciliate Tetrahymena thermophila. We have previously shown that disruption of the Tetrahymena RAD51 somatic macronuclear locus leads to defective germline micronuclear division and that conjugation of two somatic rad51 null strains results in an early meiotic arrest. We have constructed Tetrahymena strains that are capable of RAD51 expression from their parental macronuclei and are homozygous, rad51 nulls in their germline micronuclei. These rad51 null heterokaryons complete all of the early and middle stages of conjugation, including meiosis, haploid nuclear exchange, zygotic fusion, and the programmed chromosome fragmentations, sequence eliminations, and rDNA amplification that occur during macronuclear development. However, the rad51 null progeny fail to initiate the first vegetative cell division following conjugal development. Coincident with the developmental arrest is a disproportionate amplification of rDNA, despite the maintenance of normal total DNA content in the developing macronuclei. Fusion of arrested rad51 null exconjugants to wild-type cells is sufficient to overcome the arrest. Cells rescued by cytoplasmic fusion continue to divide, eventually recapitulating the micronuclear mitotic defects described previously for rad51 somatic nulls.

RAD51, the eukaryote homolog of the Escherichia coli recA, recombinase, participates in homologous recombination during mitosis, meiosis, and in the repair of double-stranded DNA breaks. The Tetrahymena thermophila RAD51 gene was recently cloned, and the in vitro activities and induction of Rad51p following DNA damage were shown to be similar to that of RAD51 from other species. This study describes the pattern of Tetrahymena RAD51 expression during both the cell cycle and conjugation. Tetrahymena RAD51 mRNA abundance is elevated during macronuclear S phase during vegetative cell growth and with both meiotic prophase and new macronuclear development during conjugation. Gene disruption of the macronuclear RAD51 locus leads to severe abnormalities during both vegetative growth and conjugation. rad51 nulls divide slowly and incur rapid deterioration of their micronuclear chromosomes. Conjugation of two rad5I nulls leads to an arrest early during prezygotic development (meiosis I). We discuss the potential usefulness of the ciliates' characteristic nuclear duality for further analyses of the potentially unique roles of Tetrahymena RAD51.