Welker D L, Hirth K P, Williams K L
Mol Cell Biol. 1985 Feb;5(2):273-80. doi: 10.1128/mcb.5.2.273-280.1985.
Wild-type isolates of Dictyostelium discoideum exhibited differences in the size of restriction fragments of the extrachromosomal 88-kilobase ribosomal DNA (rDNA) palindrome. Polymorphisms in rDNA also were found among strains derived solely from the NC4 wild-type isolate. These variations involved EcoRI fragments II, III, and V; they included loss of the EcoRI site separating fragments II and V and deletion and insertion of DNA. More than one rDNA form can coexist in the same diploid or haploid cell. However, one or another parental rDNA tended to predominate in diploids constructed, using the parasexual cycle, between haploid NC4-derived strains and haploid wild-type isolates. In some cases, most if not all of the rDNA of such diploids were of one form after ca. 50 generations of growth. Segregant haploids, derived from diploids that possessed predominantly a single rDNA allele, possessed the same allele as the diploid and did not recover the other form. This evidence implies that replication does not proceed from a single chromosomal or extrachromosomal copy of the rDNA during the asexual life cycle of D. discoideum.
盘基网柄菌的野生型分离株在染色体外88千碱基核糖体DNA（rDNA）回文序列的限制性片段大小上表现出差异。在仅源自NC4野生型分离株的菌株中也发现了rDNA的多态性。这些变异涉及EcoRI片段II、III和V；包括分隔片段II和V的EcoRI位点的缺失、DNA的缺失和插入。不止一种rDNA形式可以共存于同一个二倍体或单倍体细胞中。然而，在使用准性生殖周期构建的、介于源自单倍体NC4的菌株和单倍体野生型分离株之间的二倍体中，一种或另一种亲本rDNA往往占主导地位。在某些情况下，经过约50代生长后，此类二倍体的大部分（如果不是全部）rDNA为一种形式。源自主要拥有单一rDNA等位基因的二倍体的分离单倍体，与二倍体拥有相同的等位基因，并未恢复另一种形式。这一证据表明，在盘基网柄菌的无性生活周期中，rDNA的复制并非从单一的染色体或染色体外拷贝开始。
