Construction of a SalI/ PstI restriction map of spinach chloroplast dna using low-gelling-temperature-agarose electrophoresis

The restriction endonucleases SalI and PstI cleave circular chloroplast DNA of spinach ( Spinacia oleracea) into 12 and 10 fragments, respectively. The sum of the fragment sizes in each of the series is equivalent to the contour length of the molecule (about 95 Md). A physical map was constructed by sequential digestions using low-gelling-temperature agarose to avoid the necessity of extracting the fragments from the gel. The circular DNA molecule of spinach chloroplasts consists of two identical sequences (each about 15 Md) arranged as an inverted repeat separated by two single-copy regions of different sizes (about 52 and 13 Md).