Determination of the transcription start sites for the G. intestinalis core histone genes. A, 5'RACE analysis of the four core histone genes. The numbers at the top indicate the nucleotide positions in the DNA sequences relative to the translation start codon (overlined) for each gene. The him sequences are indicated in the grey boxes; the AT-rich sequences are indicated in the open boxes; the g-CAB elements are underlined, and the bent arrows indicate the start of transcription for each gene. B, Primer extension analysis of the H4 gene. The extension products were generated from 5'end-labeled H4/PE-1b oligonucleotide and total Giardia RNA, and the DNA sequence ladder was generated using the same end-labeled oligonucleotide as a primer. The positions of the major and minor extension products are indicated by arrows in the (+)DNA strand shown on the left.