Biomedical subjects

T W Jacobs

Publications and source records attributed to T W Jacobs.

23 records · Page 2Linked to original sources

PubMed1990

Cell division in higher plants: a cdc2 gene, its 34-kDa product, and histone H1 kinase activity in pea.

The mitotic cell cycle of yeast and animal cells is regulated by the cdc2 gene and its product, the p34 protein kinase, and by other components of the MPF or histone H1 kinase complex. We present evidence that cdc2, p34, and a histone H1 kinase also exist in higher plants. Protein extracts from 10 plant species surveyed display a 34-kDa component recognized by a monoclonal antibody directed against an evolutionarily conserved epitope of fission yeast p34. Nondenatured protein extracts of mitotic Pisum sativum (garden pea) tissues were fractionated by gel filtration, electrophoretically separated under denaturing conditions, and immunoblotted. p34 crossreactive material was apparent in both low and high molecular mass fractions, indicating that pea p34 occurs as both a monomer and as part of a high molecular mass complex. Histone H1 kinase activity was found predominantly in the higher molecular mass fractions, those to which the least phosphorylated form of pea p34 was confined. We also report the cloning of the pea homologue of cdc2 by polymerase chain reaction. DNA sequence analysis reveals perfect conservation of the hallmark "PSTAIR" sequence motif found in all cdc2 gene products analyzed to date.

Amino Acid Sequence↗

PubMed1985

Nucleotide sequence of Rhizobium meliloti 1021 nodulation genes: nodD is read divergently from nodABC.

Nodulation (nod) genes are required for Rhizobium meliloti to invade and stimulate nodule formation in its host, alfalfa. We have established the DNA sequence of nodD, nodA, and nodB, which are part of a gene cluster located 20 kb downstream of nifHDK on the R. meliloti pSym megaplasmid. The nodD open reading frame (308 amino acids) reads from proximal to nifHDK toward distal to nifHDK, divergently from nodA (196 aa) and nodB (217 aa). These two genes read from distal to nifHDK toward proximal, and are just upstream from the previously defined open reading frame for nodC. Fourteen Tn5 insertion sites have been sequenced in nodD, nodA, and nodB, revealing no major hotspots for insertion, but an overall preference for G/C bases at positions 1 and 9 of the 9-bp repeat.

Amino Acid Sequence↗

PubMed1985

Nodules are induced on alfalfa roots by Agrobacterium tumefaciens and Rhizobium trifolii containing small segments of the Rhizobium meliloti nodulation region.

Regions of the Rhizobium meliloti nodulation genes from the symbiotic plasmid were transferred to Agrobacterium tumefaciens and Rhizobium trifolii by conjugation. The A. tumefaciens and R. trifolii transconjugants were unable to elicit curling of alfalfa root hairs, but were able to induce nodule development at a low frequency. These were judged to be genuine nodules on the basis of cytological and developmental criteria. Like genuine alfalfa nodules, the nodules were initiated from divisions of the inner root cortical cells. They developed a distally positioned meristem and several peripheral vascular bundles. An endodermis separated the inner tissues of the nodule from the surrounding cortex. No infection threads were found to penetrate either root hairs or the nodule cells. Bacteria were found only in intercellular spaces. Thus, alfalfa nodules induced by A. tumefaciens and R. trifolii transconjugants carrying small nodulation clones of R. meliloti were completely devoid of intracellular bacteria. When these strains were inoculated onto white clover roots, small nodule-like protrusions developed that, when examined cytologically, were found to more closely resemble roots than nodules. Although the meristem was broadened and lacked a root cap, the protrusions had a central vascular bundle and other rootlike features. Our results suggest that morphogenesis of alfalfa root nodules can be uncoupled from infection thread formation. The genes encoded in the 8.7-kilobase nodulation fragment are sufficient in A. tumefaciens or R. trifolii backgrounds for nodule morphogenesis.

Conjugation, Genetic↗

PubMed1985

Physical and genetic map of a Rhizobium meliloti nodulation gene region and nucleotide sequence of nodC.

Infection of alfalfa by the soil bacterium Rhizobium meliloti proceeds by deformation of root hairs and bacterial invasion of host tissue by way of an infection thread. We studied an 8.7-kilobase (kb) segment of the R. meliloti megaplasmid, which contains genes required for infection. Site-directed Tn5 mutagenesis was used to examine this fragment for nodulation genes. A total of 81 R. meliloti strains with mapped Tn5 insertions in the 8.7-kb fragment were evaluated for nodulation phenotype on alfalfa plants; 39 of the insertions defined a 3.5-kb segment containing nodulation functions. Of these 39 mutants, 37 were completely nodulation deficient (Nod-), and 2 at the extreme nif-distal end were leaky Nod-. Complementation analysis was performed by inoculating plants with strains carrying a genomic Tn5 at one location and a plasmid-borne Tn5 at another location in the 3.5-kb nodulation segment. Mutations near the right border of the fragment behaved as two distinct complementation groups. The segment in which these mutations are located was analyzed by DNA sequencing. Several open reading frames were found in this region, but the one most likely to function is 1,206 bases long, reading from left to right (nif distal to proximal) and spanning both mutation groups. The genetic behavior of this segment may be due either to the gene product having two functional domains or to a recombinational hot spot between the apparent complementation groups.

Amino Acid Sequence↗

PubMedDate not supplied

Accuracy of touch imprint cytology of image-directed breast core needle biopsies.

OBJECTIVE: To evaluate the accuracy of touch imprint (TI) cytology of image-directed core needle biopsy (CNB) specimens of nonpalpable breast lesions. STUDY DESIGN: Fifty-two consecutive CNBs from 44 patients were performed under mammographic or ultrasound guidance. Air- dried TIs of CNBs were stained with Diff-Quik. TI cellularity was considered adequate if six or more ductal cell groups were identified. CNBs and TIs were interpreted in a blinded fashion. RESULTS: TI cellularity was adequate in 37/52 (71%) cases, including 17/20 carcinomas and 20/32 benign lesions. Among 17 carcinomas, TIs were positive in 12, suspicious in 4 and atypical in 1. One case of lactational change was suspicious on TI, and 5/8 fibroadenomas were atypical. No benign lesions were called "carcinoma" on cytology. When lesions categorized as "carcinoma" or "suspicious" were considered positive and those classified as "atypical" or "benign" were scored as negative, TI sensitivity and specificity were 94% and 95%, respectively. When the "atypical" cases were grouped with the positive cases, TI sensitivity was 100%, with 75% specificity. CONCLUSION: With satisfactory cellularity, TIs of CNBs are highly accurate. When immediate evaluation of CNB specimens is important, TIs can potentially decrease the number of biopsy passes required and provide preliminary diagnoses.

Biopsy, Needle↗