Fig. 2.

Nucleotide sequence of the 5′ end of the human LDL receptor gene. Nucleotide position +1 is assigned to the A of the ATG codon specifying the initiator methionine; negative numbers refer to 5′ flanking sequences. Amino acids encoded by the first exon and the position of intron 1 are indicated on the bottom line. Vertical arrows above the sequence indicate sites of transcription initiation as determined by S1 nuclease mapping (Fig. 3). Vertical arrows below the sequence indicate sites of transcription initiation as determined by primer extension (Fig. 4). Asterisks denote an apparent S1 nuclease hypersensitive site (above sequence) or a strong stop point for reverse transcriptase (below sequence). Two AT-rich regions that are located 20 to 30 nucleotides upstream of the mRNA start points are boxed. Solid horizontal arrows denote three imperfect direct repeats of 16 nucleotides each. Dashed arrows denote two imperfect inverted repeats of 14 nucleotides each. The DNA sequence was determined by a combination of the chemical (36) and enzymatic (37) methods. Two M13 subclones derived from the bacteriophage genomic clone λ34 were used as templates together with the universal primer (38) and five LDL receptor-specific oligonucleotide primers to establish the sequence by the enzymatic method. Selected regions were then sequenced again by the chemical method; 90 percent of the sequence was determined on both strands of the DNA.