TRANSCRIPTION PATTERNS OF SEQUENCES ON HUMAN-CHROMOSOME-21

The polymerase chain reaction (PCR) was used to screen embryonic, feta l and adult human cDNA libraries for transcription on chromosome 21q22 .1-->q22.3. Seventy-three pairs of oligonucleotide primers on chromoso me 21, used previously to screen a fetal brain cDNA library, were appl ied to analyze 41 different cDNA libraries. Only phage eluate (and the refore no DNA isolation) was required for this sensitive screening. Si xty primer pairs were positive with at least one cDNA library, indicat ing that the majority of primers were derived from transcribed sequenc es. Even with our most complex human fetal brain cDNA library, we dete cted only 57% (34/60) of transcribed sequences, illustrating the need to screen multiple human cDNA libraries to determine if transcription occurred. Since only 3/73 clones were present in only one cDNA library , the vast majority of transcribed sequences are present in more than one tissue.