MITOCHONDRIAL-DNA OF CHLAMYDOMONAS-REINHARDTII - THE STRUCTURE OF THEENDS OF THE LINEAR 15.8-KB GENOME SUGGESTS MECHANISMS FOR DNA-REPLICATION

The mitochondrial genome of Chlamydomonas reinhardtii is a linear doub le-stranded DNA of 15.8 kb. With the exception of the termini its DNA sequence has been published. Here we describe the unique structure of the two termini determined from cloned fragments or, for the very term inal sequences, by the Maxam and Gilbert method after 5' labeling of u ncloned terminal fragments. The 15.8-kb DNA is characterized by termin al inverted repeats of 531 or 532 bp in length including long 3' exten sions. The 3' single-stranded extensions of the left and right ends ar e non-complementary, identical in sequence, and comprise 39 to 41 nucl eotides. Remarkably, the linear genome possesses in addition an intern al 86-bp repeat of the two outermost sequences. The unusual structure of the 15.8-kb DNA termini is compared with those of other linear mito chondrial DNAs. Possible mechanisms of 15.8-kb DNA replication are dis cussed.