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B C Jensen

Publications and source records attributed to B C Jensen.

6 recordsLinked to original sources
PubMed1989

Repeat-induced G-C to A-T mutations in Neurospora.

In the Neurospora genome duplicate sequences are detected and altered in the sexual phase. Both copies of duplicate genes are inactivated at high frequency, whether or not they are linked. Restriction sites change, and affected sequences typically become heavily methylated. To characterize the alterations of the DNA, duplicated sequences were isolated before and after one or more sexual cycles. DNA sequencing and heteroduplex analyses demonstrated that the process (termed RIP) produces exclusively G-C to A-T mutations. Changes occur principally at sites where adenine is 3' of the changed cytosine. A sequence duplicated at a distant site in the genome lost approximately 10 percent of its G-C pairs in one passage through a cross. A closely linked duplication of the same sequence that was passed twice through a cross lost about half of its G-C pairs. The results suggest a mechanism for the RIP process.

Base Composition↗
PubMed1987

Rearrangement of duplicated DNA in specialized cells of Neurospora.

Introduction of DNA into Neurospora crassa can lead to sequence instability in the sexual phase of the life cycle. Sequence instability was investigated by using a set of strains transformed with single copies of a plasmid including host sequences, Neurospora sequences deleted from the host genome, and foreign sequences. The sequences already represented in the host were rearranged at high frequency in a cross. In general, both elements of the duplication, that from the plasmid and that from the host, became rearranged, whether or not they were linked. Unique sequences were left unaltered. Cytosine residues in the rearranged sequences typically became methylated de novo. Results from tetrad analyses indicated that the rearrangements occur before meiosis, during a stage between fertilization and karyogamy. We suggest that this previously unrecognized genetic process, RIP (rearrangement induced premeiotically), may contribute diversity for evolution and also maintain the gross organization of the genome.

DNA Replication↗
PubMed1987

A portable signal causing faithful DNA methylation de novo in Neurospora crassa.

Methylation of cytosine residues in eukaryotic DNA is common, but poorly understood. Typically several percent of the cytosines are methylated; however, it is unclear what governs which sequences eventually become modified. Neurospora crassa DNA containing the "zeta-eta" (zeta-eta) region, which is a region of unusually heavy methylation, was tested for its ability to direct DNA methylation de novo. DNA stripped of its methylation by propagation in Escherichia coli was reintroduced into Neurospora crassa by transformation. The zeta-eta region reproducibly became "properly" methylated whether inserted at its native chromosomal position or at ectopic sites. Adjacent Neurospora and bacterial sequences in the transforming DNA rarely became methylated. A model is presented that accounts for position-independent faithful methylation as observed in the zeta-eta region, as well as position-dependent methylation, as occasionally observed, especially with sequences not native to Neurospora.

DNA, Fungal↗