A consensus sequence for the human long interspersed repeated DNA element, L1Hs (LINE or KpnI sequence), is presented. The sequence contains two open reading frames (ORFs) which are homologous to ORFs in corresponding regions of L1 elements in other species. The L1Hs ORFs are separated by a small evolutionarily nonconserved region. The 5' end of the consensus contains frequent terminators in all three reading frames and has a relatively high GC content with numerous stretches of weak homology with AluI repeats. The 5' ORF extends for a minimum of 723 bp (241 codons). The 3' ORF is 3843 bp (1281 codons) and predicts a protein of 149 kD which has regions of weak homology to the polymerase domain of various reverse transcriptases. The 3' end of the consensus has a 208-bp nonconserved region followed by an adenine-rich end. The organization of the L1Hs consensus sequence resembles the structure of eukaryotic mRNAs except for the noncoding region between ORFs. However, due to base substitutions or truncation most elements appear incapable of producing mRNA that can be translated. Our observation that individual elements cluster into subfamilies on the basis of the presence or absence of blocks of sequence, or by the linkage of alternative bases at multiple positions, suggests that most L1 sequences were derived from a small number of structural genes. An estimate of the mammalian L1 substitution rate was derived and used to predict the age of individual human elements. From this it follows that the majority of human L1 sequences have been generated within the last 30 million years. The human elements studied here differ from each other, yet overall the L1Hs sequences demonstrate a pattern of species-specificity when compared to the L1 families of other mammals. Possible mechanisms that may account for the origin and evolution of the L1 family are discussed. These include pseudogene formation (retroposition), transposition, gene conversion, and RNA recombination.

A polymerase chain reaction-based DNA typing method, amplified fragment length polymorphism (AMP-FLP) analysis, has shown promise as a means of analyzing forensic biological evidence. A variety of DNA extraction methods were evaluated for their suitability for AMP-FLP analysis. Factors that were considered in the evaluation included DNA yield, ability of DNA to be amplified, the presence of DNA fragments other than those expected for the alleles in the sample, and differential amplification of different sized alleles for a sample. An initial screen of eight extraction methods was conducted on bloodstains deposited on cotton sheeting. These methods included Chelex | 100, organic extraction followed by Centricon 100 |

The application of deoxyribonucleic acid (DNA) typing methods for the potential identification of unknown human remains was investigated. DNA was isolated from compact bone tissue from badly decomposed bodies and from known and unknown human remains, using a decalcification and ion wash procedure. Restriction fragment length polymorphism (RFLP) analysis of variable number of tandem repeats (VNTR) loci yielded results in some cases, but more often the DNA was too degraded to produce RFLP patterns. No RFLP profiles could be obtained from putrified soft tissues. However, DNA extracted from compact bone tissue of human remains up to eleven years old was successfully amplified using the polymerase chain reaction (PCR) for the VNTR loci D1S80, D17S5, COL2A1, and APO B, as well as the HLA-DQ alpha locus. This is especially significant, since PCR results were obtained from those samples whose DNA had been degraded substantially and had yielded no RFLP patterns. All DNA types determined from the compact bone tissue from decomposed bodies whose identification had been established first by other means (and whose parents or offspring were available for typing) demonstrated mendelian inheritance of the alleles of the loci analyzed. These results suggest that amplification and typing of DNA extracted from compact bone of human remains could be useful in establishing the identity of a person, as well as in excluding possible false identifications.