The "small" polydisperse cytoplasmic extrachromosomal DNA of chicken leukaemic myeloblasts and the avian myeloblastosis virus core-bound DNA seem to descend from origin regions of chromosomal DNA replication

Nucleotide sequences are presented for 12, 7 and 12 cloned extrachromosomal DNAs by nature harbored in nucleoprotein (NP) complexes forming chicken le ukeamic myeloblast (CHLM) post microsomal sediment (POMS) components A, B a nd C, respectively, and for 11 cloned avian myeloblastosis virus (AMV) DNAs . Analysis of the abundance of sequence motifs significant for eukaryotic c hromosomal DNA replication origin (ori) regions (and their initiation zones ) has shown that these DNAs are reminiscent of cell DNA fragments enriched in ori sequences (Rao et al., 1990) and/or sequence features of several euk aryotic chromosomal oris containing clusters of modular sequence elements ( Dobbs et al., 1994). Accordingly, these DNAs, with an (A+T) content prevale ntly higher than that of the total cell DNA, revealed the presence of asymm etrically distributed (A+T)-rich stretches, scaffold attachment region (SAR ) T consensuses, polypyrimidine nucleotide (poly(Py)) tracts and minimal Sa ccharomyces cerevisiae autonomously replicating sequence (ARS) consensus, i n abundance comparable with that of these sequences of DNA fragments enrich ed in oris. All these DNAs were found to be enriched also in sequence eleme nts held as primase (Pr) attachment sites. Moreover, DNAs of POMS component B and those of AMV DNA were found to be enriched in the asymmetric pyrimid ine (qi) heptanucleotide motif of Waltz el al. (1996) occurring in the init iation zones of ori region. Consequently, these extrachromosomal DNAs, port ion of which represents a precursor of AMV DNA, seem to descent from initia tion zones of various ori regions of an early replicating chromosomal myelo blast DNA. In addition, a possible explanation of the inclination of these DNAs to form multimers is presented.