Lakshmikumaran M, Negi M S
Department of Biotechnology, Tata Energy Research Institute, New Delhi, India.
Plant Mol Biol. 1994 Mar;24(6):915-27. doi: 10.1007/BF00014445.
Restriction enzyme analysis of the rRNA genes of Eruca sativa indicated the presence of many length variants within a single plant and also between different cultivars which is unusual for most crucifers studied so far. Two length variants of the rDNA intergenic spacer (IGS) from a single individual E. sativa (cv. Itsa) plant were cloned and characterized. The complete nucleotide sequences of both the variants (3 kb and 4 kb) were determined. The intergenic spacer contains three families of tandemly repeated DNA sequences denoted as A, B and C. However, the long (4 kb) variant shows the presence of an additional repeat, denoted as D, which is a duplication of a 224 bp sequence just upstream of the putative transcription initiation site. Repeat units belonging to the three different families (A, B and C) were in the size range of 22 to 30 bp. Such short repeat elements are present in the IGS of most of the crucifers analysed so far. Sequence analysis of the variants (3 kb and 4 kb) revealed that the length heterogeneity of the spacer is located at three different regions and is due to the varying copy numbers of repeat units belonging to families A and B. Length variation of the spacer is also due to the presence of a large duplication (D repeats) in the 4 kb variant which is absent in the 3 kb variant. The putative transcription initiation site was identified by comparisons with the rDNA sequences from other plant species.
对芝麻菜rRNA基因的限制性内切酶分析表明，在单个植株内以及不同品种之间存在许多长度变异体，这对于目前研究的大多数十字花科植物来说是不寻常的。从单个芝麻菜（品种Itsa）植株中克隆并鉴定了rDNA基因间隔区（IGS）的两种长度变异体。测定了这两种变异体（3 kb和4 kb）的完整核苷酸序列。基因间隔区包含三个串联重复DNA序列家族，分别记为A、B和C。然而，长的（4 kb）变异体显示存在一个额外的重复序列，记为D，它是假定转录起始位点上游224 bp序列的重复。属于三个不同家族（A、B和C）的重复单元大小在22至30 bp范围内。到目前为止，在大多数分析过的十字花科植物的IGS中都存在这种短重复元件。对这两种变异体（3 kb和4 kb）的序列分析表明，间隔区的长度异质性位于三个不同区域，是由于属于A和B家族的重复单元拷贝数不同所致。间隔区的长度变异还归因于4 kb变异体中存在一个大的重复序列（D重复），而3 kb变异体中没有。通过与其他植物物种的rDNA序列比较，确定了假定的转录起始位点。
