Excision and replication of extrachromosomal DNA of pea (Pisum sativum)

Journal Article · Tue Feb 01 04:00:00 EST 1983 · Mol. Cell. Biol.; (United States)

DOI:https://doi.org/10.1128/MCB.3.2.172· OSTI ID:6223295

Hof, J V; Bjerknes, C A; Delihas, N C

Experiments with cultured pea roots were conducted to determine (i) whether extrachromosomal DNA was produced by cells in the late S phase or in the G2 phase of the cell cycle, (ii) whether the maturation of nascent DNA replicated by these cells achieved chromosomal size, (iii) when extrachromosomal DNA was removed from the chromosomal duplex, and (iv) the replication of nascent chains by the extrachromosomal DNA after its release from the chromosomal duplex. Autoradiography and cytophotometry of cells of carbohydrate-starved root tips revealed that extrachromosomal DNA was produced by a small fraction of cells accumulated in the late S phase after they had replicated about 80% of their DNA. Velocity sedimentation of nascent chromosomal DNA in alkaline sucrose gradients indicated that the DNA of cells in the late S phase failed to achieve chromosomal size. After reaching sizes of 70 x 10/sup 6/ to 140 x 10/sup 6/ daltons, some of the nascent chromosomal molecules were broken, presumably releasing extrachromosomal DNA several hours later. Sedimentation of selectively extracted extrachromosomal DNA either from dividing cells or from those in the late S phase showed that it replicated two nascent chains, one of 3 x 10/sup 6/ daltons and another of 7 x 10/sup 6/ daltons. Larger molecules of extrachromosomal DNA were detectable after cells were labeled for 24 h. These two observations were compatible with the idea that the extrachromosomal DNA was first replicated as an integral part of the chromosomal duplex, was cut from the duplex, and then, once free of the chromosome, replicated two smaller chains of 3 x 10/sup 6/ and 7 x 10/sup 6/ daltons. 24 references.

• Research Organization: Brookhaven National Lab., Upton, NY
• OSTI ID: 6223295
• Journal Information: Mol. Cell. Biol.; (United States), Journal Name: Mol. Cell. Biol.; (United States) Vol. 3:2; ISSN MCEBD
• Country of Publication: United States
• Language: English

Related Subjects

550400* -- Genetics
59 BASIC BIOLOGICAL SCIENCES
BIOCHEMICAL REACTION KINETICS
BIOSYNTHESIS
CELL CULTURES
CELL CYCLE
CHROMOSOMES
DNA
DNA REPLICATION
KINETICS
LEGUMINOSAE
MOLECULAR STRUCTURE
NUCLEIC ACID REPLICATION
NUCLEIC ACIDS
ORGANIC COMPOUNDS
PISUM
PLANTS
REACTION KINETICS
ROOTS
SYNTHESIS