The multigene family encoding the five classes of replication-dependent histones has been identified from the human and mouse genome sequence. The large cluster of histone genes, HIST1, on human chromosome 6 (6p21-p22) contains 55 histone genes, and Hist1 on mouse chromosome 13 contains 51 histone genes. There are two smaller clusters on human chromosome 1: HIST2 (at 1q21), which contains six genes, and HIST3 (at 1q42), which contains three histone genes. Orthologous Hist2 and Hist3 clusters are present on mouse chromosomes 3 and 11, respectively. The organization of the human and mouse histone genes in the HIST1 cluster is essentially identical. All of the histone H1 genes are in HIST1, which is spread over about 2 Mb. There are two large gaps (>250 kb each) within this cluster where there are no histone genes, but many other genes. Each of the histone genes encodes an mRNA that ends in a stemloop followed by a purine-rich region that is complementary to the 5' end of U7 snRNA. In addition to the histone genes on these clusters, only two other genes containing the stem-loop sequence were identified, a histone H4 gene on human chromosome 12 (mouse chromosome 6) and the previously described H2a.X gene located on human chromosome 11. Each of the 14 histone H4 genes encodes the same protein, and there are only three histone H3 proteins encoded by the 12 histone H3 genes in each species. In contrast, both the mouse and human H2a and H2b proteins consist of at least 10 non-allelic variants, making the complexity of the histone protein complement significantly greater than previously thought.

Disk images (bitstreams extracted from physical media) can play an essential role in the acquisition and management of digital collections by serving as containers that support data integrity and chain of custody, while ensuring continued access to the underlying bits without depending on physical carriers. Widely used today by practitioners of digital forensics, disk images can serve as baselines for comparison for digital preservation activities, as they provide fail-safe mechanisms when curatorial actions make unexpected changes to data; enable access to potentially valuable data that resides below the file system level; and provide options for future analysis. We discuss established digital forensics techniques for acquiring, preserving and annotating disk images, provide examples from both research and educational collections, and describe specific forensic tools and techniques, including an object-oriented data packaging framework called the Advanced Forensic Format (AFF) and the Digital Forensics XML (DFXML) metadata representation.

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We present performance data relating to the use of migration in a system we are creating to provide web access to heterogeneous document collections in legacy formats. Our goal is to enable sustained access to collections such as these when faced with increasing obsolescence of the necessary supporting applications and operating systems. Our system allows searching and browsing of the original files within their original contexts utilizing binary images of the original media. The system uses static and dynamic file migration to enhance collection browsing, and emulation to support both the use of legacy programs to access data and long-term preservation of the migration software. While we provide an overview of the architectural issues in building such a system, the focus of this paper is an in-depth analysis of file migration using data gathered from testing our software on 1,885 CD-ROMs and DVDs. These media are among the thousands of collections of social and scientific data distributed by the United States Government Printing Office (GPO) on legacy media (CD-ROM, DVD, floppy disk) under the Federal Depository Library Program (FDLP) over the past 20 years.