“A-Tail” Length and Transcriptional Activity of the Different Alu Subfamilies
| Alu subfamily | % Alu transcripts | % Total Alus | Transcript enrichment | Long A-Tail Alus (%) | Transcription/A-tail Factor | Expected (%) | Observed (%) |
| S + J | 66 | 82 | 0.80 | 58 (46) | 36.9 | 4 (23) | 0 (0) |
| Y | 33 | 17 | 1.96 | 34 (27) | 53.0 | 5 (33) | 5 (31) |
| Ya5 | 0.8 | 0.3 | 2.64 | 26 (21) | 54.4 | 5 (34) | 6 (38) |
| Yb8 | 0.5 | 0.2 | 2.50 | 8 (6) | 15.9 | 2 (10) | 5 (31) |
| Total | 100 | 100 | — | 126 (100) | 160.2 | 16 (100) | 16 (100) |
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↵Determined using previous data obtained from the isolation and sequencing of cDNAs derived from primary Alu transcripts (Shaikh et al. 1997).
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↵Transcript enrichment is the increase in transcript proportion relative to copy number, also referred to in the Results section as transcription rate.
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↵Data from Table 2 using the numbers of Alu elements retrieved from the human draft genome sequence with A-tail with ≥50 A.
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↵Expected is obtained using the percentage of the transcription/A-tail factor (the product of the transcript enrichment and percentage of long A-tail members) to estimate the number of Alu elements from each subfamily when there are a total of 16.
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↵Subfamily distribution of the Alu elements observed in 16 disease-causing insertions.
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↵Because of the lack of transcript detection, an estimation was made on the basis of the AluYa5 subfamily copy number.
